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1. As you might expect MySQL provides that feature too through its escape manipulator But here we want both quoting and escaping That brings us to the most widely useful manipulator string s Frank s Brand Hotdog Buns Query q conn query q lt lt SELECT FROM stock WHERE item lt lt quote lt lt s The quote manipulator both quotes strings and escapes any characters that are special in SQL 3 6 Specialized SQL Structures Retrieving data The next example introduces one of the most powerful features of MySQL Specialized SQL Structures SSQLS This is examples customl cpp include stock h include util h include lt iostream gt include lt vector gt using namespace std int main int argc char argv Wrap all MySQL interactions in one big try block so any errors are handled gracefully try Establish the connection to the database server mysqlpp Connection con mysqlpp use_exceptions if connect_to_db argc argv con return 1 Retrieve th ntire contents of the stock table and store the data in a vector of stock SSOLS structures mysqlpp Query query con query MySQL User Manual query lt lt select from stock vector lt stock gt res query storein res Display the result set print_stock_header res size vector lt stock gt iterator it for it res begin
2. I doubt anyone really needs to select rows from a table that have a prime number in a given field This example is meant to be just barely more complex than SQL can manage to avoid obscuring the point Point being the Query store_if call here gives you a container full of results meeting a criterion that you probably can t express in SQL You will no doubt have much more useful criteria in your own programs If you need a more complex query than the one store_if knows how to build when given an SSQLS examplar there are two overloads that let you use your own query string One overload takes the query string directly and the other uses the query string built with Quer y s stream interface 3 12 Executing Code for Each Row In a Result Set SQL is more than just a database query language Modern database engines can actually do some calculations on the data on the server side But this isn t always the best way to get something done When you need to mix code and a query MySQL s new Query for_each facility might be just what you need This is examples for_each cpp include util h include stock h include lt mysql h gt include lt iostream gt include lt math h gt Define a functor to collect statistics about the stock table class gather_stock_stats public gather_stock_stats items_ 0 weight_ 0 cost_ 0 void operator const stockg s items_ s num weig
3. permission In addition it is requested that 1 The modifications including deletions be noted 2 The authors be notified by email of the modification in advance of redistribution if an email address is provided in the document Mere aggregation of the MySQL User Manual with other documents or programs on the same media shall not cause this license to apply to those other works All translations derivative documents or modified documents that incorporate the MySQL User Manual may not have more restrictive license terms than these except that you may require distributors to make the resulting document available in source format 57
4. return 1 argc pop filename argument off end of list 25 MySQL User Manual try Establish the connection to the database server mysqlpp Connection con mysqlpp use_exceptions if connect_to_db argc argv con return 1 Insert image data into the BLOB column in the images table We re inserting it as an std string instead of using the raw data buffer allocated above because we don t want the data treated as a C string which would truncate the data at the first null character Query query con query query lt lt INSERT INTO images data VALUES lt lt mysqlpp escape lt lt img_data lt lt ResNSel res query execute If we get here insertion succeeded cout lt lt Inserted lt lt argvlargc lt lt into images table lt lt img_data size lt lt bytes ID lt lt res insert_id lt lt endl catch const BadQuery amp er Handle any query errors cerr lt lt Query error lt lt er what lt lt endl return 1 catch const BadConversion er Handle bad conversions cerr lt lt Conversion error lt lt er what lt lt endl lt lt tretrieved data size lt lt er retrieved lt lt actual size lt lt er actual_size lt lt endl return 1 catch const Exception amp er Catch all for any other MySQL exceptions cerr l
5. Handle bad conversions cerr lt lt Conversion error lt lt er what lt lt endl lt lt tretrieved data size lt lt er retrieved lt lt actual size lt lt er actual_size lt lt endl return 1 catch const mysgqlpp Exception amp er Catch all for any other MySQL exceptions cerr lt lt Error lt lt er what lt lt endl return 1 return 0 That s all there is to it There is one subtlety MySQL automatically quotes and escapes the data when building SQL queries using SSQLS structures It s efficient too MySQL is smart enough to apply quoting and escaping only for those data types that actually require it Because this example modifies the sample database you may want to run resetdb after running this program Modifying data It almost as easy to modify data with SSQLS This is examples custom3 cpp include stock h include util h include lt iostream gt using namespace std int main int argc char argv try Establish the connection to the database server mysqlpp Connection con mysqlpp use_exceptions if connect_to_db argc argv con return 1 Build a query to retrieve the stock item that has Unicode characters encoded in UTF 8 form mysqlpp Query query con query query lt lt select from stock where item Ntirnberger Brats Retrieve the row throwing an exception if it fai
6. MySQL User Manual Kevin Atkinson Sinisa Milivojevic Monty Widenius Warren Young Copyright O 1998 2001 2005 2007 Kevin Atkinson original author MySQL ABEducational Technology Resources Date 2007 06 28 00 17 10 0600 Thu 28 Jun 2007 Table of Contents Ls INTO dOCHO MN A a ee ON lt AA a id O peat ia 2 1 1 A Brief History ol MySQL Hb bicsscaes oe siness tlalpan 2 1 2 If Yo Have QUESOS da idas 2 DOV ELVISW visitarlo iria il iia 3 21 The Connectton Object Ad di 3 2 22 A nis senndesseoses ones ey nen seseeduedesehteednasnywadasat wed E nutes sabe eee age uvewadtsh sewer 3 23 2 A E estas PO EES 3 DAL EXCEPUONS esne vot ame donedases sue haa hacr about edhe Mace amethens har dgueaheteecusameauensneets eve ha tuaeatenn rae 4 A st taste aay ee eek Saad sta decseets wise ce doe etreaes doaed saat S 4 3 1 Running the Examples sacs lts dcir leiste reas 5 3 2 At Simple Example nit AA A 5 3 3 A More Complicated Examples ainese a a E A EE A ERE E S NER 6 SAL EXCOPUONS ER A A A NS 7 335 Quoting and ESCAPIOS seeen a e E E O EEEE EN EEEE EE INESSE 8 3 6 Specialized SQE Structures Cersi a a cz das A TEE ER Cee 9 3 7 C Equivalents of SQL Column Types ssis ereen e n aa ae EAE ITKEN R SES 15 3 8 Handime SOL Nulls irera A A E N eee tet 15 3 9 Creating Transaction Sets pidio ti corso dile 16 3 10 Which Query Ty pe to Usos it A i 18 3 11 Conditional Result Row Handling tssis ae E NEn S E NESSES Ea 19 3 12 Execut
7. Weight lt lt setw 10 lt lt Price lt lt Date lt lt endl lt lt endl Get each row in result set and print its contents mysqlpp Row row while row res fetch_row cout lt lt setw 20 lt lt row item lt lt lt lt setw 9 lt lt row num lt lt lt lt setw 9 lt lt row weight lt lt lt lt setw 9 lt lt row price lt lt lt lt setw 9 lt lt row sdate lt lt endl return 0 else cerr lt lt Failed to get stock item lt lt query error lt lt endl return 1 This example does the same thing as simple2 only with a use query instead of a store query If your program uses exceptions you should instead look at examples usequery cpp which does the same thing as simple3 but with exception awareness 3 11 Conditional Result Row Handling Query store is fine if you really need all the rows the query returns It sometimes happens that you can t express the full selection criteria in a SQL query Instead of storing the full result set then picking over it to find the rows you want to keep use Query store_if This is examples store_if cpp include util h include stock h include lt mysql h gt include lt iostream gt include lt math h gt 19 MySQL User Manual Define a functor for testing primality struct is_prime bool operator const stock
8. amp s if s num 2 s num 3 return true 2 and 3 are trivial cases else if s num lt 2 s num 2 0 return false can t be prime if lt 2 or even else The only possibility left is that it s divisible by an odd number that s less or equal to its square root for int i 3 i lt sqrt double s num i 2 if s num i 0 return false return true y int main int argc char argv try Connect to the sample database mysqlpp Connection con if connect_to_db argc argv con return 1 Collect the stock items with prime quantities std vector lt stock gt results mysqlpp Query query con query query store_if results stock is_prime Show the results print_stock_header results size std vector lt stock gt const_iterator it for it results begin it results end 1t print_stock_row it gt item c_str it gt num it gt weight it gt price it gt sdate catch const mysqlpp BadQuery e Something went wrong with the SQL query std cerr lt lt Query failed lt lt e what lt lt std endl return 1 20 MySQL User Manual catch const mysqlpp Exceptiong er Catch all for any other MySQL exceptions std cerr lt lt Error lt lt er what lt lt std endl return 1 return 0
9. The defaults are suitable for building SQL queries but if you re using these methods in a different context you may need to override these defaults For instance you could use these methods to dump data to a text file using different delimiters and quoting rules than SQL At this point we ve seen all the major aspects of the SSQLS feature The final sections of this chapter look at some of the peripheral aspects 5 6 Alternate Creation Methods If for some reason you want your SSQLS data members to have different names than used in the MySQL database you can do so like this sql_create_c_names_5 stock 1 5 string item item int num quantity double weight weight double price price mysqlpp Date date shipment If you want your SSQLS to have its data members in a different order from those in the MySQL table you can do it like this sql_create_c_order_5 stock 2 5 mysqlpp Date date 5 double price 4 string item 1 int num 2 double weight 3 You can combine the custom names and custom ordering like this sql_create_complete_5 stock 2 5 mysqlpp date date shipment 5 double price price 4 string item item 1 int num quantity 2 double weight weight 3 All three of these macro types have basic variants that work the same way Again basic SSQLSes lack the features necessary for automatic insert update and replace query creation 5 7 Expanding
10. flags operate independently There s no way to globally enable or disable this flag on existing objects in a single call If you re using the NoExceptions feature and you re still seeing optional exceptions thrown you disabled exceptions on the wrong object The exception thrower could be unrelated to the object you disabled exceptions on it could be its parent or it could be a child created before you changed the exception throwing flag Some of the exceptions MySQL can throw are not optional e The largest set of non optional exceptions are those from the Standard C Library For instance if your code said row 21 on a row containing only 5 fields the std vector underlying the row object will throw an exception It will that is if it conforms to the standard You might consider wrapping your program s main loop in a try block catching std exceptions just in case you trigger one of these exceptions e ColData will always throw BadConversion when you ask it to do an improper type conversion For example you ll get an exception if you try to convert 1 25 to int but not when you convert 1 00 to int In the latter case MySQL knows that it can safely throw away the fractional part e Ifyou use template queries and don t pass enough parameters when instantiating the template Query will throw a BadParamCount exception e Ifyou pass a bad option value to Connection set_option it will throw a BadOpt ion exception It s
11. insert is implemented more or less like this this lt lt INSERT INTO lt lt v table lt lt lt lt v field list lt lt VALUES lt lt v value_list lt lt where v is the SSQLS you re asking the Query object to insert into the database Now let s look at a complete example which uses one of the more complicated forms of equal_list This example builds a query with fewer hard coded strings than the most obvious technique requires which makes it more robust in the face of change Here is examples custom5 cpp include stock h include util h include lt iostream gt include lt vector gt using namespace std int main int argc char argv try mysqlpp Connection con mysqlpp use_exceptions if connect_to_db argc argv con return 1 37 MySQL User Manual Get all the rows in the stock table mysqlpp Query query con query query lt lt select from stock vector lt stock gt res query storein res if res size gt 0 Build a select query using the data from the first row returned by our previous query query reset query lt lt select from stock where lt lt res 0 equal_list and stock_weight stock_price Display the finished query cout lt lt Custom query n lt lt query preview lt lt endl catch const mysqlpp BadQuery er Handle any query err
12. so you still need to be aware of these underlying issues During the development of the Plan 9 operating system a kind of successor to Unix Ken Thompson invented the UTF 8 encoding UTF 8 is a superset of 7 bit ASCII and is compatible with C strings since it doesn t use O bytes anywhere as multi byte Unicode encodings do As a result many programs that deal in text will cope with UTF 8 data even though they have no explicit support for UTF 8 Follow the last link above to see how the design of UTF 8 allows this Thus when explicit support for Unicode was added in MySQL va 1 they chose to make UTF 8 the native encoding to preserve backward compatibility with programs that had no Unicode support 6 2 Unicode on Unixy Systems Linux and Unix have system wide UTF 8 support these days If your operating system is of 2001 or newer vintage it probably has such support On such a system the terminal I O code understands UTF 8 encoded data so your program doesn t require any special code to correctly display a UTF 8 string If you aren t sure whether your system supports UTF 8 natively just run the 42 MySQL User Manual Wee tt simplel example if the first item has two high ASCII characters in place of the ii in N rnberger Brats you know it s not handling UTF 8 If your Unix doesn t support UTF 8 natively it likely doesn t support any form of Unicode at all for the historical reasons I gave above Therefore you will h
13. Iterate through the result set 4 Goto2 There is however a lot of extra functionality along each step of the way 2 1 The Connection Object A Connection object manages the connection to the MySQL server You need at least one of these objects to do anything Because the other MySQL objects your program will use often depend at least indirectly on the Connection instance the Connection object needs to live at least as long as all other MySQL objects in your program 2 2 The Query Object Most often you create SQL queries using a Query object created by the Connection object Query is subclassed from std stringstream which means you can write to it like any other C stream to form a query The library includes stream manipulators that make it easy to generate syntactically correct SQL You can also set up Template Queries with this class Template queries work something like C s printf function you set up a fixed query string with tags inside that indicate where to insert the variable parts If you have multiple queries that are structurally similar you simply set up one template query and use that in the various locations of your program A third method for building queries is to use Query with Specialized SQL Structures SSQLS This feature presents your results as a C data structure instead of making you access the data through MySQL intermediary classes It also reduces the amount of embedded SQL code your prog
14. change have higher numbers so we don t always have to pass them We can just give them defaults and take those defaults when applicable This is most useful when some parameters in a template query vary less often than other parameters For example 31 MySQL User Manual query def field1 item query def field2 price Result resl query store Hamburger Buns item Result res2 query store 1 25 price This stores the result of the following queries in res1 and res2 respectively select item price from stock where item Hamburger Buns select item price from stock where price 1 25 Default parameters are useful in this example because we have two queries to issue and parameters 2 and 3 remain the same for both while parameters O and 1 vary Some have been tempted into using this mechanism as a way to set all of the template parameters in a query query def what Hamburger Buns query def wheref item query def field1 item query def field2 price Result resl query store This can work but it is not designed to In fact it s known to fail horribly in one common case You will not get sympathy if you complain on the mailing list about it not working If your code doesn t actively reuse at least one of the parameters in subsequent queries you re abusing MySQL 4 and it is likely to take its revenge on you 4 5 Error Handling If for some reason you di
15. data size lt lt er retrieved lt lt actual size lt lt er actual_size lt lt endl return 1 catch const mysqlpp Exceptiong er Catch all for any other MySQL exceptions cerr lt lt Error lt lt er what lt lt endl return 1 return 0 When you run the example you will notice that in the WHERE clause only the item field is checked for This is because SSQLS also also less than comparable 13 MySQL User Manual Don t forget to run resetdb after running the example Less than comparable SSQLS structures can be sorted and stored in STL associative containers as demonstrated in the next example This 1s examples custom4 cpp include stock h include util h include lt iostream gt using namespace std int main int argc char argv try Establish the connection to the database server mysqlpp Connection con mysqlpp use_exceptions if connect_to_db argc argv con return 1 Retrieve all rows from the stock table and put them in an STL set Notice that this works just as well as storing them in a vector which we did in customl cpp It works because SSQLS objects are less than comparable mysqlpp Query query con query query lt lt select from stock set lt stock gt res query storein res Display the result set Since it is an STL set and we set up the SSQLS to compare b
16. educational to modify the examples to force exceptions For instance misspell a field name use an out of range index or change a type to force a ColData conversion error 3 5 Quoting and Escaping SQL syntax often requires certain data to be quoted Consider this query SELECT FROM stock WHERE item Hotdog Buns Because the string Hotdog Buns contains a space it must be quoted With MySQL you don t have to add these quote marks manually string s Hotdog Buns Query q conn query q lt lt SELECT FROM stock WHERE item lt lt quote_only lt lt s That code produces the same query string as in the previous example We used the MySQL quote_only manipulator which causes single quotes to be added around the next item inserted into the stream This works for various string MySQL User Manual types for any type of data that can be converted to MySQL s ColData type and for Specialized SQL Structures The next section introduces the SSQLS feature Quoting is pretty simple but SQL syntax also often requires that certain characters be escaped Imagine if the string in the previous example was Frank s Brand Hotdog Buns instead The resulting query would be SELECT FROM stock WHERE item Frank s Brand Hotdog Buns That s not valid SQL syntax The correct syntax is SELECT FROM stock WHERE item Frank s Brand Hotdog Buns
17. from the example table and prints those values out Notice that MySQL s Result objects work similarly to the STL std vector container The only trick is that you can t use subscripting notation if the argument is ever 0 because of the way we do overloading so it s safer to call at instead The only thing that isn t explicit in the code above is that we delegate command line argument parsing and connection establishment to connect_to_db in the util module This function exists to give the examples a consistent interface not to hide important details 3 3 A More Complicated Example The simple1 example above was pretty trivial Let s get a little deeper Here is examples simple2 cpp include util h include lt mysql h gt include lt iostream gt include lt iomanip gt using namespace std int main int argc char argv MySQL User Manual Connect to the sample database mysqlpp Connection con false if connect_to_db argc argv con return 1 Retrieve the sample stock table set up by resetdb mysqlpp Query query con query query lt lt select from stock mysqlpp Result res query store Display results if res Display header cout setf ios left cout lt lt setw 21 lt lt Item lt lt setw 10 lt lt Num lt lt setw 10 lt lt Weight lt lt setw 10 lt lt Price lt lt Date lt lt endl lt l
18. lt res names size i cout lt lt setw 2 lt lt i this is the name of the field lt lt setw 15 lt lt res names i c_str this is the SQL identifier nam Result types unsigned int returns a mysql_type_info which in many ways is like type_info except that it has additional sql type information in it with one of the methods being sql_name lt lt setw 15 lt lt res types i sql_name this is the C identifier name which most closely resembles the sql name its is implementation defined and often not very readable lt lt setw 20 lt lt res types 1 name lt lt endl cout lt lt endl 23 MySQL User Manual if res types 0 typeid string this is demonstrating how a mysql_type_info can be compared with a C type_info cout lt lt Field item is of an SQL type which most Closely resembles nthe C string type n if res types 1 typeid longlong cout lt lt Field num is of an SQL type which most closely resembles nCt long long int type n else if res types 1 base_type typeid longlong you have to be careful as if it can be null the actual type is Null lt TYPE gt not TYPE So you should always use the base_type method to get at the underlying type If the type is not null than this base type would be the same as its type cout lt lt Field num
19. of this data for each row but that would be quite wasteful 44 MySQL User Manual Beware of some of the more obscure ways this can happen For example Connection c Query q c query Result res q store Row row res at 0 res q store At this point the row variable s contents are likely no longer usable The program may run but the row object will use data field names etc from the second query not the first 8 Incompatible Library Changes This chapter documents those library changes since the epochal 1 7 9 release that break end user programs You can dig this stuff out of the ChangeLog but the ChangeLog focuses more on explaining and justifying the facets of each change while this section focuses on how to migrate your code between these library versions Since pure additions do not break programs those changes are still documented only in the ChangeLog 8 1 API Changes v1 7 10 v1 7 19 v1 7 20 v2 0 0 This section documents files functions methods and classes that were removed or changed in an incompatible way If your program uses the changed item you will have to change something in your program to get it to compile after upgrading to each of these versions Removed Row operator overloads except the one for size_type and added Row lookup_by_name to provide the subscript by string functionality In practical terms this change means that the row
20. requires that any application supplied function or table used by this function must be optional if the application does not supply 1t the square root function must still compute square roots These requirements apply to the modified work as a whole If identifiable sections of that work are not derived from the Library and can be reasonably considered independent and separate works in themselves then this License and its terms do not apply to those sections when you distribute them as separate works But when you distribute the same sections as part of a whole which is a work based on the Library the distribution of the whole must be on the terms of this License whose permissions for other licensees extend to the entire whole and thus to each and every part regardless of who wrote it Thus it is not the intent of this section to claim rights or contest your rights to work written entirely by you rather the intent is to exercise the right to control the distribution of derivative or collective works based on the Library In addition mere aggregation of another work not based on the Library with the Library or with a work based on the Library on a volume of a storage or distribution medium does not bring the other work under the scope of this License 3 You may opt to apply the terms of the ordinary GNU General Public License instead of this License to a given copy of the Library To do this you must alter all the notices that refer to
21. useful 32 MySQL User Manual 5 1 sql_create This is the most basic sort of SSQLS declaration sql_create_5 stock 1 0 string item int num double weight double price mysqlpp Date date This creates a C structure called stock containing five member variables item num weight price and date along with some constructors and other member functions useful with MySQL One of the generated constructors takes a reference to a mysqlpp Row object allowing you to easily populate a vector of stocks like so vector lt stock gt result query storein result That s all there is to it The only requirements are that the table structure be compatible with the SSQLS s member variables and that the fields are in the same order The general format of this set of macros is sql_create_ NAMI GI COMPCOUNT SETCOUNT TYPE1 ITEM1 TYPE ITEM Where is the number of member variables NAME is the name of the structure you wish to create TYPEx is the type of a member variable and I TEMx is that variable s name The COMPCOUNT and SETCOUNT arguments are described in the next section 5 2 SSQLS Comparison and Initialization sql_create_x adds member functions and operators to each SSQLS that allow you to compare one SSQLS instance to another These functions compare the first COMPCOUNT fields in the structure In the example above COMPCOUNT is 1 so only the it
22. where it should have in v1 7 This bug is fixed in v2 0 If your program begins crashing due to uncaught exceptions after upgrading to v2 0 this is the most likely cause The most expeditious fix in this situation is to use the new NoExceptions feature to return these code paths to the v1 7 behavior A better fix is to rework your program to avoid or deal with the new exceptions All custom MySQL exceptions now derive from the new Exception interface The practical upshot of this is that the variability between the various exception types has been eliminated For instance to get the error string the BadQuery exception had a string member called error plus a method called what Both did the same thing and the what method is more common so the error string was dropped from the interface None of the example programs had to be changed to work with the new exceptions so if your program handles MySQL exceptions the same way they do your program won t need to change either Renamed SOLQueryNEParams exception to BadParamCount to match style of other exception names Added BadOption ConnectionFailed DBSelectionFailed EndOfResults EndOfResultSets LockFailed and ObjectNotInitialized exception types to fix overuse of BadQuery Now the latter is used only for errors on query execution If your program has a catch all block taking a std exception for each try block containing MySQL statements you probably won t need to change your pr
23. 1 according to one report There doesn t seem to be a practical limit with GCC 3 3 at least I set the limit to 100 and the only thing that happened is that custom macros h went from 1 3 MB to 18 MB and the build time for examples custom got a lot longer 5 9 SSQLS and BLOB Columns It takes special care to use SSQLS with BLOB columns It s safest to declare the SSQLS field as of type mysqlpp sql_blob This is currently a typedef alias for ColData which is the form the data is in just before the SSQLS mechanism populates the structure Thus when the data is copied from the internal MySQL data structures into your SSQLS you get a direct copy of the ColData object s contents without interference Because ColData derives from std string and C strings handle binary data just fine you might think you can use std string instead of sql_blob but the current design of ColData converts to std string viaa C string As a result the BLOB data is truncated at the first embedded null character during population of the SSQLS There s no way to fix that without completely redesigning either ColData or the SSQLS mechanism The sql_blob typedef may be changed to alias a different type in the future so using it instead of ColData ensures that your code tracks these library changes automatically Besides ColData is only intended to be an internal mechanism within MySQL The only reason the layering is so thin here is because it s the only way to pr
24. MySQL In early August of 2004 the current maintainer Warren Young got fed up with this situation and took over He released 1 7 10 later that month 1 2 If You Have Questions If you want to email someone to ask questions about this library we greatly prefer that you send mail to the MySQL mailing list The mailing list is archived so if you have questions do a search to see if the question has been asked before MySQL User Manual You may find people s individual email addresses in various files within the MySQL distribution Please do not send mail to them unless you are sending something that is inherently personal Not all of the principal developers of MySQL are still active in its development those who have dropped out have no wish to be bugged about MySQL Those of us still active in MySQL development monitor the mailing list so you aren t getting any extra coverage by sending messages to additional email addresses 2 Overview MySQL has developed into a very complex and powerful library with many different ways to accomplish the same task Unfortunately this means that figuring out how to perform a simple task can be frustrating for new users In this section we will provide an overview of the most important user facing components of the library The overall process for using MySQL is similar to that of most other database access APIs 1 Open the connection 2 Form and execute the query 3
25. MySQL User Manual mysqlpp Connection con mysqlpp use_exceptions if connect_to_db argc argv con return 1 Retrieve a subset of the stock table and store the data in a vector of stock_subset SSQLS structures mysqlpp Query query con query query lt lt select item from stock vector lt stock_subset gt res query storein res Display the result set cout lt lt We have lt lt endl vector lt stock_subset gt iterator it for it res begin it res end it cout lt lt Xt lt lt it gt item lt lt endl catch const mysqlpp BadQuery er Handle any query errors cerr lt lt Query error lt lt er what lt lt endl return 1 catch const mysqlpp BadConversion er Handle bad conversions e g type mismatch populating stock cerr lt lt Conversion error lt lt er what lt lt endl lt lt tretrieved data size lt lt er retrieved lt lt actual size lt lt er actual_size lt lt endl return 1 catch const mysgqlpp Exception amp er Catch all for any other MySQL exceptions cerr lt lt Error lt lt er what lt lt endl return 1 return 0 See the simple example in the Tutorial for another way to accomplish the same thing This example illustrates an important point you could not use the 5 member stock structure in this example The re
26. SSQLS Macros If you ever need to see the code that a given SSQLS declaration expands out to use the utility doc ssqls pretty like so doc ssqls pretty lt myprog cpp less 39 MySQL User Manual This Perl script locates the first SSQLS declaration in that file then uses the C preprocessor to expand that macro The script assumes that your system s preprocessor is called cpp and that its command line interface follows Unix conventions If you run it from the top MySQL directory as shown above it will use the header files in the distribution s 1ib subdirectory Otherwise it assumes the MySQL headers are in their default location usr include mysql If you want to use headers in some other location you ll need to change the directory name in I flag at the top of the script 5 8 Extending the SSQLS Mechanism The SSQLS headers custom h and custom macros h are automatically generated by the Perl script custom pl Although it is possible to change this script to get additional functionality it s usually better to do that through inheritance A regular user may find it helpful to change the the limit on the maximum number of SSQLS data members allowed It s 25 out of the box A smaller value may speed up compile time or you may require a higher value because you have more complex tables than that Simply change the max_data_members variable at the top of custom pl and say make The limit for Visual C is 3
27. TCOUNT values cannot be equal If they are the macro will generate two initialization constructors with identical parameter lists which is illegal in C Why does this happen It s often convenient to be able to say something like x stock Hotdog This requires that there be a constructor taking COMPCOUNT arguments to create the temporary stock instance used in the comparison It is easy to work around this limitation Using our stock example structure if you wanted comparisons to consider all 5 fields and also be able to initialize all 5 fields at once you would pass 5 for COMPCOUNT and 0 for SETCOUNT You would still get a 5 parameter initialization constructor and a 5 parameter set function 5 3 Retrieving a Table Subset It s not necessary to retrieve an entire table row using SSQLS as long as the fields you want are grouped together at the start of the table schema examples custom6 cpp illustrates this include util h include lt mysql h gt include lt custom h gt include lt iostream gt Ju nclude lt iomanip gt include lt vector gt using namespace std To store a subset of a row we define an SSQLS containing just the fields that we will store There are complications here that are covered in the user manual sql_create_1 stock_subset Li 107 string item int main int argc char argv try Establish the connection to the database server 34
28. User Manual return 1 Show initial state mysqlpp Query query con query cout lt lt Initial state of stock table lt lt endl print_stock_table query Insert a few rows in a single transaction set mysqlpp Transaction trans con stock rowl Sauerkraut 42 1 2 0 75 2006 03 06 query insert rowl query execute query reset stock row2 Bratwurst 24 3 0 4 99 2006 03 06 query insert row2 query execute query reset cout lt lt nRows are inserted but not committed lt lt endl cout lt lt Verify this with another program e g simplel then hit Enter lt lt endl getchar cout lt lt nCommitting transaction gives us lt lt endl trans commit print_stock_table query Now let s test auto rollback mysqlpp Transaction trans con cout lt lt nNow adding catsup to the database lt lt endl stock row Catsup 3 3 9 2 99 2006 03 06 query insert row query execute query reset cout lt lt nNo yuck We don t like catsup Rolling it back lt lt endl print_stock_table query catch const mysqlpp BadQuery er Handle any query errors cerr lt lt Query error lt lt er what lt lt endl return 1 catch const mysqlpp BadConversiong er Handle bad conversions 17 MySQL User Manual cerr lt lt Co
29. _double price mysqlpp sql_date sdate As you can see SSQLS is very powerful It allows you to have a C structure paralleling your SQL table structure and use it easily with STL code Adding data SSQLS can also be used to add data to a table This is examples custom2 cpp include stock h include util h include lt iostream gt using namespace std int main int argc char argv try Establish the connection to the database server mysqlpp Connection con mysqlpp use_exceptions if connect_to_db argc argv con return 1 Create and populate a stock object We could also have used the set member which takes the same parameters as this constructor stock row Hot Dogs 100 1 5 1 75 1998 09 25 Form the query to insert the row into the stock table mysqlpp Query query con query query insert row Show the query about to be executed cout lt lt Query lt lt query preview lt lt endl Execute the query We us xecute because INSERT doesn t return a result set query execute Print the new table mysqlpp Result res get_stock_table query res print_stock_rows res catch const mysqlpp BadQuery er Handle any query errors cerr lt lt Query error lt lt er what lt lt endl return 1 11 MySQL User Manual catch const mysqlpp BadConversiong er
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31. ary where it will be okay to break the ABI Until then we re stuck with it If the MySQL server keeps rejecting your template queries try explicitly casting the parameters to SOLSt ring query storein my_vector SQLString 1 This ensures that your code calls one of the overloads meant to handle template query parameters I don t recommend doing this habitually because it will clutter your code For the most part MySQL s interface is set up to do the right thing It s just that there are still a few corner cases that can t be fixed until the next time we can redesign the interface 4 4 Default Parameters The template query mechanism allows you to set default parameter values You simply assign a value for the parameter to the appropriate position in the Query def array You can refer to the parameters either by position or by name query def 1 item query def wheref item Both do the same thing This mechanism works much like C s default function parameter mechanism if you set defaults for the parameters at the end of the list you can call one of Query s query execution methods without passing all of the values If the query takes four parameters and you ve set defaults for the last three you can execute the query using as little as just one explicit parameter Now you can see why we numbered the template query parameters the way we did a few sections earlier We ordered them so that the ones less likely to
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33. ased on the item column the rows will be sorted by item print_stock_header res size set lt stock gt iterator it cout precision 3 for it res begin it res end it print_stock_row it gt item c_str it gt num it gt weight it gt price it gt sdate Use set s find method to look up a stock item by item name This also uses the SSQLS comparison setup it res find stock Hotdog Buns if it res end cout lt lt endl lt lt Currently lt lt it gt num lt lt hotdog buns in stock lt lt endl else cout lt lt endl lt lt Sorry no hotdog buns in stock lt lt endl 14 MySQL User Manual catch const mysqlpp BadQuery er Handle any query errors cerr lt lt Query error lt lt er what lt lt endl return 1 catch const mysqlpp BadConversiong er Handle bad conversions cerr lt lt Conversion error lt lt er what lt lt endl lt lt tretrieved data size lt lt er retrieved lt lt actual size lt lt er actual_size lt lt endl return 1 catch const mysgqlpp Exception amp er Catch all for any other MySQL exceptions cerr lt lt Error lt lt er what lt lt endl return 1 return 0 For more details on the SSQLS feature see the Specialized SQL Structures chapter 3 7 C Equivalents of SQL Col
34. ason is when you assign a Row object to an SSQLS the function that copies the row s data into the structure expects to see as many fields in the row as are in the SSQLS Your program will crash when the code tries to access fields beyond those that exist in the Row object The converse is not true however if you change the SELECT statement above so that it retrieves more than one column the code will still work because the extra fields in each row will simply be ignored Realize that the second and third parameters to sq1_create_1 can t be anything other than 1 and 0 respectively As discussed above the second parameter must be at least 1 but since there is only one field in the structure it cannot be higher than 1 Since the third parameter cannot be equal to the second only 0 works there 5 4 Additional Features of Specialized SQL Structures 35 MySQL User Manual Up to this point we haven t been using all of the features in the SSQLS structures we ve been generating We could have used the sql_create_basic_ macros instead which would have worked just as well for what we ve seen so far and the generated code would have been smaller Why is it worth ignoring the basic variants of these macros then Consider this query insert s This does exactly what you think it does it inserts s into the database This is possible because a standard SSQLS has functions that the query object can call to get the list of fields a
35. ave to convert the UTF 8 data to the local 8 bit character set The standard Unix function iconv can help here If your system doesn t have the iconv facility there is a free implementation available from the GNU Project Another library you might check out is IBM s ICU This is rather heavy weight so if you just need basic conversions iconv should suffice 6 3 Unicode on Windows Each Windows API function that takes a string actually comes in two versions One version supports only 1 byte ANSI characters a superset of ASCII so they end in A Windows also supports the 2 byte subset of Unicode called UCS 2 Some call these wide characters so the other set of functions end in W The MessageBox API for instance is actually a macro not a real function If you define the UNICODE macro when building your program the MessageBox macro evaluates to MessageBoxW otherwise to MessageBoxA Since MySQL uses the UTF 8 Unicode encoding and Windows uses UCS 2 you must convert data when passing text between MySQL and the Windows API Since there s no point in trying for portability no other OS I m aware of uses UCS 2 you might as well use platform specific functions to do this translation Since version 2 2 2 MySQL ships with two Visual C specific examples showing how to do this in a GUI program In earlier versions of MySQL we did Unicode conversion in the console mode programs but this was unrealistic How
36. base type is of an SQL type which most closely nresembles the C long long int type n catch const BadQuery amp er Handle any query errors cerr lt lt Query error lt lt er what lt lt endl return 1 catch const BadConversion er Handle bad conversions cerr lt lt Conversion error lt lt er what lt lt endl lt lt tretrieved data size lt lt er retrieved lt lt actual size lt lt er actual_size lt lt endl return 1 catch const Exception amp er Catch all for any other MySQL exceptions cerr lt lt Error lt lt er what lt lt endl return 1 return 0 3 14 Dealing with Binary Data The tricky part about dealing with binary data in MySQL is to ensure that you don t ever treat the data as a C string which is really easy to do accidentally C strings treat zero bytes as special end of string characters but they re not special at all in binary data Recent releases of MySQL do a better job of letting you keep data in forms that don t have this problem but it s still possible to do it incorrectly These examples demonstrate correct techniques Loading a binary file into a BLOB column This example shows how to insert binary data into a MySQL table s BLOB column with MySQL and also how to get the value of the auto increment column from the previous insert This MySQL feature is usually us
37. cal invocation is exrun resetdb localhost root nunyabinness For resetdb the user name needs to be for an account with permission to create databases Once the database is created you can use any account that has read and write permissions for the sample database mysql_cpp_data You may also have to re run reset db after running some of the other examples as they change the database 3 2 A Simple Example The following example demonstrates how to open a connection execute a simple query and display the results This is examples simplel cpp tinclude util h include lt mysql h gt include lt iostream gt include lt iomanip gt using namespace std int main int argc char argv MySQL User Manual Connect to the sample database mysqlpp Connection con false if connect_to_db argc argv con return 1 Retrieve a subset of the sample stock table set up by resetdb mysqlpp Query query con query query lt lt select item from stock mysqlpp Result res query store Display the result set cout lt lt We have lt lt endl if res mysqlpp Row row mysqlpp Row size_type i for i 0 row res at i i cout lt lt t lt lt row at 0 lt lt endl else cerr lt lt Failed to get item list lt lt query error lt lt endl return 1 return 0 This example simply gets the entire item column
38. d not specify all the parameters when executing the query and the remaining parameters do not have their values set via Query def the query object will throw a BadParamCount object If this happens you can get an explanation of what happened by calling BadParamCount what like so query def fieldi item query def field2 price Result res query store 1 25 This would throw BadParamCount because the wheref is not specified In theory this exception should never be thrown If the exception is thrown it probably a logic error in your program 5 Specialized SQL Structures The Specialized SQL Structure SSQLS feature lets you easily define C structures that match the form of your SQL tables Because of the extra functionality that this feature builds into these structures MySQL can populate them automatically when retrieving data from the database with queries returning many records you can ask MySQL to populate an STL container of your SSQLS records with the results When updating the database MySQL can use SSQLS structures to match existing data and it can insert SSQLS structures directly into the database You define an SSQLS using one of several macros These are in the file custom h and in the file that it includes custom macros h There are a bunch of different macros for different purposes The following sections will discuss each macro type separately beginning with the easiest and most generally
39. dgs pete ER E r coetish teases ptee stor eO ep dees 39 5 1 Expanding SSOLS Macro ui oidos 39 3 3 Extending the SSQLS Mechanism ascefS deceesedecseenuee sa a ter e E S sede ceteney Ge teessen gece 40 5 9 SSQLS and BLOB Columns iii dd aida ii 40 6 Using Unicode with My QE ue told station inde cea serpientes 42 6 1 A Short History ob Unicode iii A eager ula eins eae tee dhe eel ees 42 6 2 Unicode on Unixy SyStemS ue ss5 csngascag eet dssacv estes a Sse cevtaectyeetaseds eed dep eseed denn E E E NSARE 42 6 3 Unicode on WINdOWS 3 A A E eve depots 43 AA O deepenevenes tues 44 7 Important Underlying C API Limitations 2 0 0 0 cee cee ce ee ce eeca ceca eene eens ecu eeneeeeneeeeeeseaeeeaeeeges 44 8 Incompatible Library Changes esemes daedenbemen ad cutace dou nsden sant daa o A S E begosetiee EEEa 45 Ssh API Chan IES on ce a Dies 45 8 2 ABUL Chan es mesos erp tt vote tase sees gp nte Bogs NE oie chee rte 48 A E nesi r whe ar e e E eee Sch wes oe irdeto E abu von ea devine lat onda deh uate a gee an eeu ute 49 9 1 GNU Lesser General Public License armadas poy satenng wen feina dowstyee tbasgs deis 50 9 2 MySQL User Manual License 20 00 00 cece cee E aN ceca ceca cece eens E EEEO EESE PECA E 37 1 Introduction MySQL is a powerful C wrapper for MySQL s C API Its purpose is to make working with queries as easy as working with STL containers The latest version of MySQL can be found at the official web site Support
40. dl cerr lt lt http server name com cgi bin cgi_jpeg id 2 lt lt endl cerr lt lt endl cerr lt lt This will retrieve the image with ID 2 lt lt endl cerr lt lt endl cerr lt lt You will probably have to change some of the defines at the top of lt lt endl cerr lt lt examples cgi_jpeg cpp to allow the lookup to work lt lt endl return 1 Connection con use_exceptions try con connect IMG_DATABASE IMG_HOST IMG_USER IMG_PASSWORD Query query con query query lt lt SELECT FROM images WHERE id lt lt img_id ResUse res query use if res images img res fetch_row 27 MySQL User Manual cout lt lt Content type image jpeg lt lt endl cout lt lt Content length lt lt img data length lt lt n n cout lt lt img data else cout lt lt Content type text plain lt lt endl lt lt endl cout lt lt ERROR No such image with ID lt lt img_id lt lt endl catch const BadQuery amp er Handle any query errors cout lt lt Content type text plain lt lt endl lt lt endl cout lt lt QUERY ERROR lt lt er what lt lt endl return 1 catch const Exception amp er Catch all for any other MySQL exceptions cout lt lt Content type text plain lt lt endl lt lt endl cout lt lt GENERAL ERROR l
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43. e to use the new Connection Option enumerated values accept a true return value as meaning success instead of 0 and use the proper argument type Regarding the latter read_option took a const char argument but because it was just a thin wrapper over the MySQL C API function mysql options the actual value being pointed to could be any of several types This new mechanism is properly type safe Exception related changes Classes Connection Query Result ResUse and Row now derive from OptionalExceptions which gives these classes a common interface for disabling exceptions In addition almost all of the per method exception disabling flags were removed The preferred method for disabling exceptions on these objects is to create an instance of the new NoExceptions class on the stack which disables exceptions on an OptionalExceptions subclass as long as the NoExceptions instance is in scope You can instead call disable_exceptions on any of these objects but if you only want them disabled temporarily it s easy to forget to re enable them later In the previous version of MySQL those classes that supported optional exceptions that could create instances of other such classes were supposed to pass this flag on to their children That is if you created a Connection object with exceptions enabled and then asked it to create a Query object the Query object also had exceptions disabled The problem is this didn t happen in all cases
44. ecommend making it free software that everyone can redistribute and change You can do so by permitting redistribution under these terms or alternatively under the terms of the ordinary General Public License To apply these terms attach the following notices to the library It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty and each file should have at least the copyright line and a pointer to where the full notice is found lt one line to give the library s name and a brief idea of what it does gt Copyright O lt year gt lt name of author gt 55 MySQL User Manual This library is free software you can redistribute it and or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation either version 2 1 of the License or at your option any later version This library is distributed in the hope that it will be useful but WITHOUT ANY WARRANTY without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE See the GNU Lesser General Public License for more details You should have received a copy of the GNU Lesser General Public License along with this library if not write to the Free Software Foundation Inc 59 Temple Place Suite 330 Boston MA 02111 1307 USA Also add information on how to contact you by electronic and paper mail You should also get your employer i
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46. ed to create 24 MySQL User Manual unique IDs for rows as they re inserted The program requires one command line parameter over that required by the other examples you ve seen so far the path to a JPEG file This is examples load_jpeg cpp tinclude util h include lt mysql h gt include lt fstream gt using namespace std using namespace mysqlpp static bool is_jpeg const unsigned char img_data return img_data 0 OxFF amp amp img_data 1 0xD8 amp amp memcmp img_data 6 JFIF 4 0 memcmp img_data 6 Exif 4 0 int main int argc char argv Assume that the last command line argument is a file Try to read that file s data into img_data and check it to see if it appears to be a JPEG file Bail otherwise string img_data if arge gt 1 amp amp argv 1 0 ifstream img_file argv arge 1 ios ate if img_file size_t img_size img_file tellg if img_size gt 10 img_file seekg 0 ios beg char img_buffer new char img_size img_file read img_buffer img_size if is_Jpeg unsigned char img_buffer img_data assign img_buffer img_size else cerr lt lt File does not appear to be a JPEG lt lt endl delete img_buffer else cerr lt lt File is too short to be a JPEG lt lt endl if img_data empty print_usage argv 0 jpeg_file
47. em field will be checked when comparing two stock structures This feature works best when your table s key fields are the first ones in the table schema and you set COMPCOUNT equal to the number of key fields That way a check for equality between two SSQLS structures in your C code will give the same results as a check for equality in SQL COMPCOUNT must be at least 1 The current implementation of sql_create_x cannot create an SSQLS without comparison member functions Because our stock structure is less than comparable you can use it in STL algorithms and containers that require this such as STL s associative containers std set lt stock gt result query storein result cout lt lt result lower_bound stock Hamburger gt item lt lt endl 33 MySQL User Manual This will print the first item in the result set that begins with Hamburger The third parameter to sql_create_x is SETCOUNT If this is nonzero it adds an initialization constructor and a set member function taking the given number of arguments for setting the first N fields of the structure For example you could change the above example like so sql_create_5 stock 1 2 string item int num double weight double price mysqlpp Date date stock foo Hotdog 52 In addition to this 2 parameter constructor this version of the stock SSQLS will have a similar 2 parameter set member function The COMPCOUNT and SE
48. ers combined than that alone Add in all the other languages of the world plus the various symbols people use in writing and you have a real mess Since no standards body held sway over things like international character encoding in the early days of computing many different character sets were invented These character sets weren t even standardized between operating systems so heaven help you if you needed to move localized Greek text on a DOS box to a Russian Macintosh The only way we got any international communication done at all was to build standards on top of the common 7 bit ASCII subset Either people used approximations like a plain c instead of the French or they invented things like HTML entities amp ccedil in this case to encode these additional characters using only 7 bit ASCII Unicode solves this problem It encodes every character used for writing in the world using up to 4 bytes per character The subset covering the most economically valuable cases takes two bytes per character so most Unicode aware programs deal in 2 byte characters for efficiency Unfortunately Unicode was invented about two decades too late for Unix and C Those decades of legacy created an immense inertia preventing a widespread move away from 8 bit characters MySQL and C come out of these older traditions and so they share the same practical limitations MySQL doesn t have a reason to do anything more than just pass data along unchanged
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50. event BLOB data from being corrupted while staying within the current library interface design You can see this technique in action in the cgi_jpeg example include lt mysql h gt include lt custom h gt using namespace std using namespace mysqlpp define IMG_DATABASE mysql_cpp_data define IMG_HOST localhost define IMG_USER Yoot define IMG_PASSWORD nunyabinness sql_create_2 images Ly 2 40 MySQL User Manual 3 ysqlpp sql_int_unsigned id mysqlpp sql_blob data int main unsigned int img_id 0 char cgi_query getenv QUERY_STRING if cgi_query if strlen cgi_query lt 4 memcmp cgi_query id 3 cout lt lt Content type text plain lt lt endl lt lt endl cout lt lt ERROR Bad query string lt lt endl return 1 else img_id atoi cgi_query 3 else cerr lt lt Put this program into a web server s cgi bin directory then lt lt endl cerr lt lt invoke it with a URL like this lt lt endl cerr lt lt endl eerr lt lt http server name com cgi bin cgi_jpeg id 2 lt lt endl cerr lt lt endl cerr lt lt This will retrieve the image with ID 2 lt lt endl cerr lt lt endl cerr lt lt You will probably have to change some of the defines at the top of lt lt endl cerr lt lt examples cgi_jpeg cpp to allow the lookup to work lt l
51. f you work as a programmer or your school if any to sign a copyright disclaimer for the library if necessary Here is a sample alter the names Yoyodyne Inc hereby disclaims all copyright interest in the library Frob a library for tweaking knobs written by James Random Hacker lt signature of Ty Coon gt 1 April 1990 Ty Coon President of Vice That s all there is to it 56 MySQL User Manual 9 2 MySQL User Manual License I COPYRIGHT The copyright to the MySQL User Manual is owned by its authors ll LICENSE The MySQL User Manual may be reproduced and distributed in whole or in part in any medium physical or electronic provided that this license notice is displayed in the reproduction Commercial redistribution is permitted and encouraged Thirty days advance notice via email to the authors of redistribution is appreciated to give the authors time to provide updated documents A REQUIREMENTS OF MODIFIED WORKS All modified documents including translations anthologies and partial documents must meet the following requirements 1 The modified version must be labeled as such 2 The person making the modifications must be identified 3 Acknowledgement of the original author must be retained 4 The location of the original unmodified document be identified 5 The original authors names may not be used to assert or imply endorsement of the resulting document without the original authors
52. field syntax no longer works you must use the new lookup_by_name method instead Renamed the generated library on POSIX systems from libsqlplus to libmysqlpp Removed SQLQuery operator and the same for its Query subclass Use the copy constructor instead if you need to copy one query to another query object The library used to have two names for many core classes a short one such as Row and a longer one MysqlRow The library now uses the shorter names exclusively All symbols within MySQL are in the mysqlpp namespace now if you use the new mysql h header If you use the older sqlplus hh or mysql hh headers these symbols are hoist up into the global namespace The older headers cause the compiler to emit warnings if you use them and they will go away someday Connection class changes 45 MySQL User Manual Connection create_db and drop_db return true on success They returned false in v1 7 x This change will only affect your code if you have exceptions disabled Renamed Connection real_connect to connect made several more of its parameters default and removed the old connect method as it s now a strict subset of the new one The only practical consequence 1s that 1f your program was using real_connect you will have to change it to connect Replaced Connection read_option with new set_option mechanism In addition to changing the name programs using this function will hav
53. for MySQL can be had on the mailing list That page hosts the mailing list archives and tells you how you can subscribe 1 1 A Brief History of MySQL MySQL was created in 1998 by Kevin Atkinson It started out MySQL specific but there were early efforts to try and make it database independent and call it SQL This is where the old library name sqlplus came from This is also why the old versions prefixed some class names with Mysql but not others the others were supposed to be the database independent parts Then in 1999 Sinisa Milivojevic unofficially took over maintenance of the library releasing versions 1 0 and 1 1 All of Kevin s releases were pre 1 0 point releases Kevin gave over maintenance to Sinisa officially with 1 2 and ceased to have any involvement with the library s maintenance Sinisa went on to maintain the library through 1 7 9 released in mid 2001 Since Sinisa is an employee of MySQL AB it seems to be during this time that the dream of multiple database compatibility died With version 1 7 9 MySQL went into a period of stasis lasting over three years During this time Sinisa ran the MySQL mailing list and supported its users but made no new releases There were many patches submitted during this period some of which were ignored others which were just put on the MySQL web site for people to try A lot of these patches were mutually incompatible and not all of them gave a fully functional copy of
54. ht_ s num s weight cost_ s num s price private 21 MySQL User Manual mysqlpp sql_bigint items_ mysqlpp sql_double weight_ cost_ friend std ostream amp operator lt lt std ostream amp os const gather_stock_stats g ss y Dump the contents of gather_stock_stats to a stream in human readable form std ostream amp operator lt lt std ostream os const gather_stock_statsg ss os lt lt ss items_ lt lt items lt lt weighing lt lt ss weight_ lt lt stone and lt lt costing lt lt ss cost_ lt lt cowrie shells return os int main int argc char argv try Connect to the sample database mysqlpp Connection con if connect_to_db argc argv con return 1 Gather and display the stats for the entire stock table mysqlpp Query query con query std cout lt lt There are lt lt query for_each stock gather_stock_stats lt lt lt lt std endl catch const mysqlpp BadQuery e Something went wrong with the SQL query std cerr lt lt Query failed lt lt e what lt lt std endl return 1 catch const mysqlpp Exception amp er Catch all for any other MySQL exceptions std cerr lt lt Error lt lt er what lt lt std endl return 1 return 0 You only need to read the main function to get a go
55. ing Code for Each Row In a Result Set oooocccccccccncccnccnnconnconnconncnnnconnconnconncnnnccnncnnncnns 21 3 13 Getting Field Meta Information sregep neeesa E ceca sean EEEE RE EER EE 23 3 14 Dealing with Binary Data iii a Te Gon ck TEE ened E E as dias 24 A Template QUERES sisin ea aea a ea a a deus a ae inicia SE eT E tues 28 4l Seting up Template QUES ee en dolo ee E o E EE e E r TEER vee ers 29 4 2 Setting the Parameters at Execution Time oooccnoccnnccnnconnconecnnncnnocnnocnnrnnnrnnconnccnnoronccnnconncnnncnnnes 30 4 3 Parameter Types and Function Overloads oooccoccnoccnnccnnccnnconoconecnnncnnncnnnrnnronconccnnccnnccnnccnnccnncos 31 AA Detault Parameters socus ineess ost asec wes devsawes hess E dco deuneder Sensedesagehanense gute segaubedet oaveanatacwedawestens 31 AS Error Handling 2 2 ici et A eet elle is eee Tee RS 32 3 Specialized SQL STHUCtUIES rniosan r taninos ternas rn UnA e Ea EEE En N RES 32 A ges op A A gee dey SUL eae ee a 33 5 2 SSQLS Comparison and Initialization 2 0 0 0 cece cence cece cece cece ne ceneeeneeeeeeeeseeesaeeeaeeea sean eeues 33 5 3 Retneving a Table Subset nic es keel heed EAN E SERE senda gle ca e EE lvoe ees obey EE RENS 34 5 4 Additional Features of Specialized SQL Structures ooocccnccnnccnnccnncnnnconconoconononnnnnronncnnccnncinninnno 35 5 5 Harnessing SSQ S Internals iones Ws dened lus o as 36 MySQL User Manual 3 6 Alternate Creation Methods aereos earn a gesbeeen
56. it res end it print_stock_row it gt item it gt num it gt weight it gt price it gt sdate catch const mysqlpp BadQuery er Handle any query errors cerr lt lt Query error lt lt er what lt lt endl return 1 catch const mysqlpp BadConversiong er Handle bad conversions e g type mismatch populating stock cerr lt lt Conversion error lt lt er what lt lt endl lt lt tretrieved data size lt lt er retrieved lt lt actual size lt lt er actual_size lt lt endl return 1 catch const mysgqlpp Exception amp er Catch all for any other MySQL exceptions cerr lt lt Error lt lt er what lt lt endl return 1 return 0 Here is the stock h header used by that example and many others include lt mysql h gt include lt custom h gt include lt string gt The following is calling a very complex macro which will create struct stock which has the member variables sql_char item te sql_date sdate plus methods to help populate the class from a MySQL row See the SSQLS sections in the user manual for further details sql_create_5 stock 1 5 The meaning of these values is covered in the user manual mysqlpp sql_char item mysqlpp sql_bigint num mysqlpp sql_double weight 10 MySQL User Manual mysqlpp sql
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58. libraries in order to permit linking those libraries into non free programs When a program is linked with a library whether statically or using a shared library the combination of the two is legally speaking a combined work a derivative of the original library The ordinary General Public License therefore 50 MySQL User Manual permits such linking only if the entire combination fits its criteria of freedom The Lesser General Public License permits more lax criteria for linking other code with the library We call this license the Lesser General Public License because it does Less to protect the user s freedom than the ordinary General Public License It also provides other free software developers Less of an advantage over competing non free programs These disadvantages are the reason we use the ordinary General Public License for many libraries However the Lesser license provides advantages in certain special circumstances For example on rare occasions there may be a special need to encourage the widest possible use of a certain library so that it becomes a de facto standard To achieve this non free programs must be allowed to use the library A more frequent case is that a free library does the same job as widely used non free libraries In this case there is little to gain by limiting the free library to free software only so we use the Lesser General Public License In other cases permission to use a particular libr
59. list lt Manip gt value_list cchar d Manip m bool il bool i2 false bool i5 false const List form template lt class Manip gt stock_cus_value_list lt Manip gt value_list cchar d Manip m stock_enum il stock_enum i2 stock_NULL stock_enum i5 stock_NULL const 36 MySQL User Manual Vector form template lt class Manip gt stock_cus_value_list lt Manip gt value_list cchar d Manip m vector lt bool gt i const Plus the obvious equivalents for field list and equal_list Rather than try to learn what all of these methods do at once let s ease into the subject Consider this code stock s Dinner Rolls 75 0 95 0 97 1998 05 25 cout lt lt Value list lt lt s value_list lt lt endl cout lt lt Field list lt lt s field _list lt lt endl cout lt lt Equal list lt lt s equal_list lt lt endl That would produce something like Value list Dinner Rolls 75 0 95 0 97 1998 05 25 Field list item num weight price date Equal list item Dinner Rolls num 75 weight 0 95 price 0 97 date 1998 05 25 That is a value list is a list of data member values within a particular SSQLS instance a field list is a list of the fields columns within that SSQLS and an equal list is a list in the form of an SQL equals clause Just knowing that much it shouldn t surprise you to learn that Query
60. ls mysqlpp Result res query store if res empty throw mysqlpp BadQuery UTF 8 bratwurst item not found in table run resetdb 12 MySQL User Manual Because there should only be one row in the result set there s no point in storing the result in an STL container We can store the first row directly into a stock structure because one of an SSQLS s constructors takes a Row object stock row res at 0 Create a copy so that the replace query knows what the original values are stock orig_row row Change the stock object s item to use only 7 bit ASCII and to deliberately be wider than normal column widths printed by print_stock_table row item Nuerenberger Bratwurst Form the query to replace the row in the stock table query update orig_row row Show the query about to be executed cout lt lt Query lt lt query preview lt lt endl Run the query with execute since UPDATE doesn t return a result set query execute Print the new table contents get_stock_table query res print_stock_rows res catch const mysqlpp BadQuery er Handle any query errors cerr lt lt Query error lt lt er what lt lt endl return 1 catch const mysqlpp BadConversion er Handle bad conversions cerr lt lt Conversion error lt lt er what lt lt endl lt lt tretrieved
61. n instance is when the private section was declared before the public section it is now the opposite way This can change the object s layout in memory so a program linking to the library must be rebuilt Simplified the date and time class hierarchy Date used to derive from mysql_date Time used to derive from mysql_time and DateTime used to derive from both of those All three of these classes used to derive from mysql_dt_base All of the mysql1_ classes functionality and data has been folded into the leaf classes and now the only thing shared between them is their dependence on the DTbase template Since the leaf classes interface has not changed and end user code shouldn t have been using the other classes this shouldn t affect the API in any practical way mysql_type_info now always initializes its private num member Previously this would go uninitialized if you used the default constructor Now there is no default ctor but the ctor taking one argument which sets num has a default 9 Licensing The primary copyright holders on the MySQL library and its documentation are Kevin Atkinson 1998 MySQL AB 1999 through 2001 and Educational Technology Resources Inc 2004 through the date of this writing There are other contributors who also retain copyrights on their additions see the ChangeLog file in the MySQL distribution tarball for details The MySQL library and its Reference Manual are released under the GNU Lesser Ge
62. nd such which it uses to build an insert query query update and query replace also rely on this SSQLS feature A basic SSQLS lacks these functions Another feature of standard SSQLSes you might find a use for is changing the table name used in queries By default the table in the MySQL database is assumed to have the same name as the SSQLS structure type But if this is inconvenient you can globally change the table name used in queries like this stock table MyStockData 5 5 Harnessing SSQLS Internals Continuing the discussion in the previous section there is a further set of methods that the non basic versions of the sql_create macros define for each SSQLS These methods are mostly for use within the library but some of them are useful enough that you might want to harness them for your own ends Here is some pseudocode showing how the most useful of these methods would be defined for the stock structure used in all the custom cpp examples Basic form template lt class Manip gt stock_value_list lt Manip gt value_list cchar d a anip m mysqlpp quote const template lt class Manip gt stock_field _list lt Manip gt field list cchar d O anip m mysqlpp do_nothing const template lt class Manip gt stock_equal_list lt Manip gt equal_list cchar d cchar e Manip m mysqlpp quote const Boolean argument form template lt class Manip gt stock_cus_value_
63. neral Public License LGPL reproduced below The MySQL User Manual excepting some example code from the library reproduced within it is offered under a license closely based on the Linux Documentation Project License LDPL v2 0 included below The MySQL documentation isn t actually part ofthe Linux Documentation Project so the main changes are to LDP related language Also generic language such as author s or authors has been replaced with specific language because the license applies to only this one document These licenses basically state that you are free to use distribute and modify these works whether for personal or commercial purposes as long as you grant the same rights to those you distribute the works to whether you changed them or not See the licenses below for full details 49 MySQL User Manual 9 1 GNU Lesser General Public License Version 2 1 February 1999 Copyright C 1991 1999 Free Software Foundation Inc 59 Temple Place Suite 330 Boston MA 02111 1307 USA Everyone is permitted to copy and distribute verbatim copies of this license document but changing it is not allowed This is the first released version of the Lesser GPL It also counts as the successor of the GNU Library Public License version 2 hence the version number 2 1 Preamble The licenses for most software are designed to take away your freedom to share and change it By contrast the GNU General Public Licens
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65. ns MySQL User Manual Some of these exceptions are optional When exceptions are disabled on a MySQL object it signals errors in some other way typically by returning an error code or setting an error flag Classes that support this feature derive from OptionalExceptions Moreover when such an object creates another object that also derives from this interface it passes on its exception flag Since everything flows from the Connection object disabling exceptions on it at the start of the program disables all optional exceptions You can see this technique at work in the simple 1 3 examples which keeps them well simple Real world code typically can t afford to lose out on the additional information and control offered by exceptions But at the same time it is still sometimes useful to disable exceptions temporarily To do this put the section of code that you want to not throw exceptions inside a block and create a NoExceptions object at the top of that block When created it saves the exception flag of the Opt ionalExceptions derivative you pass to it and then disables exceptions on it When the NO0Except ions object goes out of scope at the end of the block it restores the exceptions flag to its previous state See examples resetdb cpp to see this technique at work When one OptionalExceptions derivative passes its exceptions flag to another such object it is only passing a copy This means that the two objects
66. nversion error lt lt er what lt lt endl lt lt tretrieved data size lt lt er retrieved lt lt lt lt er actual_size lt lt endl actual size return 1 catch const mysgqlpp Exception amp er Catch all for any other MySQL exceptions cerr lt lt Error lt lt er what lt lt endl return 1 return 0 3 10 Which Query Type to Use There are three major ways to execute a query in MySQL Query execute Query store and Query use Which should you use and why execute is for queries that do not return data per se For instance CREATE INDEX You do get back some information from the MySQL server which execute returns to its caller in a ResNSel object In addition to the obvious a flag stating whether the query succeeded or not this object also contains things like the number of rows that the query affected If you only need the success status there s Query exec which just returns bool If your query does pull data from the database the simplest option is store This returns a Result object which contains an in memory copy of the result set The nice thing about this is that Result is a sequential container like std vector so you can iterate through it forwards and backwards access elements with subscript notation etc There are also the storein methods which actually put the result set into an STL container of y
67. od idea of what the program does The key line of code passes an SSQLS examplar and a functor to Query for_each for_each uses the SSQLS instance to build a select from TABLI E query stock in this case It runs that query internally calling gather_stock_stats on each row This is a pretty contrived example you could actually do this in SQL but we re trying to prevent the complexity of the code from getting in the way of the demonstration here 22 MySQL User Manual Just as with store_if described above there are two other overloads for for_each that let you use your own query string 3 13 Getting Field Meta Information The following example demonstrates how to get information about the fields in a result set such as the name of the field and the SQL type This is examples fieldinfl cpp include util h include lt mysql h gt include lt iostream gt include lt iomanip gt using namespace std using namespace mysqlpp int main int argc char argv ERYiA Connection con use_exceptions if connect_to_db argc argv con return 1 Query query con query query lt lt select from stock cout lt lt Query lt lt query preview lt lt endl Result res query store cout lt lt Records Found lt lt res size lt lt endl lt lt endl cout lt lt Query Info n cout setf ios left for unsigned int i 0 i
68. ode with the library you must provide complete object files to the recipients so that they can relink them with the library after making changes to the library and recompiling it And you must show them these terms so they know their rights We protect your rights with a two step method 1 we copyright the library and 2 we offer you this license which gives you legal permission to copy distribute and or modify the library To protect each distributor we want to make it very clear that there is no warranty for the free library Also if the library is modified by someone else and passed on the recipients should know that what they have is not the original version so that the original author s reputation will not be affected by problems that might be introduced by others Finally software patents pose a constant threat to the existence of any free program We wish to make sure that a company cannot effectively restrict the users of a free program by obtaining a restrictive license from a patent holder Therefore we insist that any patent license obtained for a version of the library must be consistent with the full freedom of use specified in this license Most GNU software including some libraries is covered by the ordinary GNU General Public License This license the GNU Lesser General Public License applies to certain designated libraries and is quite different from the ordinary General Public License We use this license for certain
69. ogram Otherwise the new exceptions will likely show up as program crashes due to unhandled exceptions Query class changes In previous versions Connection had a querying interface similar to class Query s These methods were intended only for Query s use no example ever used this interface directly so no end user code is likely to be affected by this change A more likely problem arising from the above change is code that tests for query success by calling the Connection object s success method or by casting it to bool This will now give misleading results because queries no longer go through the Connection object Class Query has the same success testing interface so use it instead 46 MySQL User Manual e Query now derives from std ostream instead of std stringstreanm Result ResUse class changes e Renamed ResUse mysql_result to raw_result so it s database server neutral e Removed ResUse eof as it wrapped the deprecated and unnecessary MySQL C API function mysql eof See the simple3 and usequery examples to see the proper way to test for the end of a result set Row class changes e Removed field name form of Row field_list It was pointless e Row subscripting works more like v1 7 9 one can subscript a Row with a string e g row myfield or with an integer e g row 5 lookup_by_name was removed Because row 0 is ambiguous 0 could mean the first field or be a null pointe
70. or lt mystruct gt v Query q connection query q lt lt SELECT FROM mytable q storein v for vector lt mystruct gt iterator it v begin it v end 1t cout lt lt Price lt lt it gt price lt lt endl Isn t that slick 2 4 Exceptions By default the library throws exceptions whenever it encounters an error You can ask the library to set an error flag instead if you like but the exceptions carry more information Not only do they include a string member telling you why the exception was thrown there are several exception types so you can distinguish between different error types within a single try block 3 Tutorial MySQL User Manual This tutorial is meant to give you a jump start in using MySQL While it is a very complicated and powerful library 1t s possible to make quite functional programs without tapping but a fraction of its power This section will introduce you to the most useful fraction This tutorial assumes you know C fairly well in particular the Standard Template Library STL and exceptions 3 1 Running the Examples All of the examples are complete running programs If you built the library from source the examples should have been built as well If you installed it via the RPM package the example source code and a simplified Makefile is in the examples subdirectory of the mysql devel package s documentation directory This is usually
71. ors cerr lt lt Query error lt lt er what lt lt endl return 1 catch const mysqlpp BadConversiong er Handle bad conversions cerr lt lt Conversion error lt lt er what lt lt endl lt lt tretrieved data size lt lt er retrieved lt lt actual size lt lt er actual_size lt lt endl return 1 catch const mysgqlpp Exception amp er Catch all for any other MySQL exceptions cerr lt lt Error lt lt er what lt lt endl return 1 return 0 This example uses the list form of equal_list The arguments stock_weight and stock_price are enum values equal to the position of these columns within the stock table sql_create_x generates this enum for you automatically The boolean argument form of that equal_list call would look like this query lt lt select from stock where lt lt res 0 equal_list and false false true true false It s a little more verbose as you can see And if you want to get really complicated use the vector form vector lt bool gt v 5 false v stock_weight true v stock_price true query lt lt select from stock where lt lt 38 MySQL User Manual res 0 equal_list and v This form makes the most sense if you are building many other queries and so can re use that vector object Many of these methods accept manipulators and custom delimiters
72. our choice The downside of these methods is that a sufficiently large result set will give your program memory problems For these large result sets the superior option is a use query This returns a ResUse object which is similar to Result but without all of the random access features This is because a use query tells the database server to send the results back one row at a time to be processed linearly It s analogous to a C stream s input iterator as opposed to a random access iterator that a container like vector offers By accepting this limitation you can process arbitrarily large result sets This technique is demonstrated in examples simple3 cpp include util h include lt mysql h gt include lt iostream gt include lt iomanip gt using namespace std int main int argc char argv Connect to the sample database mysqlpp Connection con false if connect_to_db argc argv con return 1 18 MySQL User Manual Ask for all rows from the sample stock table set up by resetdb Unlike simple2 example we don t store result set in memory mysqlpp Query query con query query lt lt select from stock mysqlpp ResUse res query use Retreive result rows one by one and display them if res Display header cout setf ios left cout lt lt setw 21 lt lt Item lt lt setw 10 lt lt Num lt lt setw 10 lt lt
73. pe NullisZero or NullisBlank Consider this code mysqlpp Null lt unsigned char mysqlpp NullisZero gt myfield myfield mysqlpp null cout lt lt myfield lt lt endl int x myfield cout lt lt x lt lt endl This will print 0 twice If you had used the default for the second Nul 1 template parameter the first output statement would have printed NULL and the second would have thrown a BadNullConversion exception 3 9 Creating Transaction Sets MySQL v2 1 added the Transaction class which makes it easier to use transactions in an exception safe manner Normally you create the Transaction object on the stack before you issue the queries in your transaction set Then when all the queries in the transaction set have been issued you call Transaction commit which commits the transaction set If the Transaction object goes out of scope before you call commit the transaction set is rolled back This ensures that if some code throws an exception after the transaction is started but before it is committed the transaction isn t left unresolved examples xaction cpp illustrates this include stock h include util h include lt transaction h gt include lt iostream gt using namespace std int main int argc char argv try Establish the connection to the database server mysqlpp Connection con mysqlpp use_exceptions if connect_to_db argc argv con 16 MySQL
74. pertinent obligations then as a consequence you may not distribute the Library at all For example if a patent license would not permit royalty free redistribution of the Library by all those who receive copies directly or indirectly through you then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Library If any portion of this section is held invalid or unenforceable under any particular circumstance the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims this section has the sole purpose of protecting the integrity of the free software distribution system which is implemented by public license practices Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system it is up to the author donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License 54 MySQL User Manual 12 If the distribution and or use of the Library is restricted in certain countries either by patents or by copyright
75. proper declaration for MySQL would be mysqlpp Null lt mysqlpp sql_tinyint_unsigned gt myfield Template instantiations are first class types in the C language on par with any other type You can use Null template instantiations anywhere you d use the plain version of that type You can see a complete list of Nu1 1 template instantiations for all column types that MySQL understands at the top of 1ib type_info cpp 15 MySQL User Manual There s a secondary distinction between SQL null and anything available in the standard C type system SQL null is a distinct value equal to nothing else We can t use C s NULL for this because it is ambiguous being equal to 0 in integer context MySQL provides the global null object which you can assign to a Nul1 template instance to make it equal to SQL null myfield mysqlpp null The final aspect of MySQL s null handling is that by default it will enforce the uniqueness of the SQL null value If you try to convert a SQL null to a plain C data type MySQL will throw a BadNullConversion exception If you insert a SQL null into a C stream you get NULL If you don t like this behavior you can change it by passing a different value for the second parameter to template Nu11 By default this parameter is NullisNull meaning that we should enforce the uniqueness of the null type To relax this distinction you can instantiate the Nul1 template with a different behavior ty
76. r to const char there is now Row at which can look up any field by index Miscellaneous changes v2 2 0 e Where possible all distributed Makefiles only build dynamic libraries Shared objects on most Unices DLLs on Windows etc Unless your program is licensed under the GPL or LGPL you shouldn t have been using the static libraries from previous versions anyway e Removed the backwards compatibility headers sqlplus hh and mysql hh If you were still using these you will have to change to mysql h which will put all symbols in namespace mysqlpp e Can no longer use arrow operator gt on the iterators into the Fields Result and Row containers Code like this will have to change Query q con query q lt lt delete from mytable where myfield 0 myvalue q parse q def myvalue some_value q execute to something more like this Query q con query q lt lt delete from mytable where myfield 0 q parse q execute some_value The first code snippet abuses the default template query parameter mechanism Query def to fill out the template instead of using one of the overloaded forms of execute store or use taking one or more SOLSt ring parameters The purpose of Query def is to allow for default template parameters over multiple queries In the first snippet above there is only one parameter so in order to justify the use of template queries in the fi
77. ram needs 2 3 Result Sets The field data in a result set are stored in a special std string like class called ColData This class has conversion operators that let you automatically convert these objects to any of the basic C data types Additionally MySQL defines classes like DateTime which you can initialize from a MySQL DATETIME string These automatic conversions are protected against bad conversions and can either set a warning flag or throw an exception depending on how you set the library up As for the result sets as a whole MySQL has a number of different ways of representing them MySQL User Manual Queries That Do Not Return Data Not all SQL queries return data An example is CREATE TABLE For these types of queries there is a special result type ResNSel that simply reports the state resulting from the query whether the query was successful how many rows it impacted if any etc Queries That Return Data Dynamic Method The easiest way to retrieve data from MySQL uses a Result object which includes one or more Row objects Because these classes are std vector like containers you can treat the result set as a two dimensional array For example you can get the 5th item on the 2nd row by simply saying result at 1 at 4 You can also access row elements by field name like this result at 2 price An alternate way of accessing your query results is through a ResUse object This class act
78. rst place it must be changing with each query Therefore it isn t really a default parameter at all We did not make this change maliciously but you can understand why we are not in any hurry to restore this feature Incidentally this change was made to allow better support for BLOB columns 47 MySQL User Manual v2 3 0 Connection set_option calls now set the connection option immediately instead of waiting until just before the connnection is actually established Code that relied on the old behavior could see unhandled exceptions since option setting errors are now thrown from a different part of the code You want to wrap the actual set_option call now not Connection connect FieldNames and FieldTypes are no longer exported from the library If you are using these classes directly from Visual C or MinGW your code won t be able to dynamically link to a DLL version of the library any more These are internal classes however so no one should be using them directly 8 2 ABI Changes This section documents those library changes that require you to rebuild your program so that it will link with the new library Most of the items in the previous section are also ABI changes but this section is only for those items that shouldn t require any code changes in your program If you were going to rebuild your program after installing the new library anyway you can probably ignore this section v1 7 18 The Q
79. s are complete since the NET platform handles a lot of things behind the scenes for us We don t need any error checking code for such simple routines All of this assumes you re using Windows NT or one of its direct descendants Windows 2000 Windows XP Windows Vista or any Server variant of Windows Windows 95 and its descendants 98 ME and CE do not support UCS 2 They still have the W APIs for compatibility but they just smash the data down to 8 bit and call the A version for you 6 4 For More Information The Unicode FAQs page has copious information on this complex topic When it comes to Unix and UTF 8 specific items the UTF 8 and Unicode FAQ for Unix Linux is a quicker way to find basic information 7 Important Underlying C API Limitations Since MySQL is built on top of the MySQL C API libmysqlclient it shares all of its limitations The following points out some of these limitations that frequently bite newbies Some of these may be papered over at the MySQL layer in future releases but it s best to write your program as if they were permanent fixtures of the universe l Only one active query per connection This one bites MySQL newbies most often in multithreaded programs If the program has only one Connection object and each thread gets their Query objects from it it s inevitable that one of those query objects will try to execute while another query is already running on that single connection The safe
80. s more like an STL input iterator than a container you walk through your result set one item at a time always going forward You can t seek around in the result set and you can t know how many results are in the set until you find the end This method is more efficient when there can be arbitrarily many results which could pose a memory allocation problem with the previous technique Queries That Return Data Static Method The Specialized SQL Structures SSQLS feature method above defines C structures that match the table structures in your database schema We call it the static method because the table structure is fixed at compile time Indeed some schema changes require that you update your SSQLS definitions and recompile or else the program could crash or throw bad conversion exceptions when MySQL tries to stuff the new data into an outdated data structure Not all changes require a recompile Adding a column to a table is safe for instance as the program will ignore the new column until you update the SSQLS definition The advantage of this method is that your program will require very little embedded SQL code You can simply execute a query and receive your results as C data structures which can be accessed just as you would any other structure The results can be accessed through the Row object or you can ask the library to dump the results into a sequential or set associative STL container for you Consider this vect
81. ser Manual To set up a template query you simply insert it into the Query object using numbered placeholders wherever you want to be able to change the query Then you call the parse function to tell the Query object that the query string 1s a template query and it needs to parse it query lt lt select 2 fieldl 3 field2 from stock where l wheref S0Oq what query parse The format of the placeholder is SHE modifier name Where HHF is a number up to three digits It is the order of parameters given to a SQLQueryParms object starting from 0 modifier can be any one of the following Print an actual 9 vote Don t quote or escape no matter what q This will quote and escape the item using the MySQL C API function mysql escape string if it is a string or char or another MySQL specific type that needs to be quoted Q Quote but don t escape based on the same rules as for q This can save a bit of processing time if you know the strings will never need quoting r Always quote and escape even if it is a number R Always quote but don t escape even if it is a number name is for an optional name which aids in filling SQLQueryParms Name can contain any alpha numeric characters or the underscore You can have a trailing colon which will be ignored If you need to represent an actual colon after the name follow the name with two colons The first one will end
82. st course is to have a separate Connection object per thread and for your code to get Query objects in a thread only from that thread s Connection object Alternately you can confine MySQL database access to a single thread You must consume all rows from a query before you can start a new query This one bites MySQL newbies most often when they try code like this Connection c Query q c query Result rl q use Result r2 q use T select garbage from plink where foobie tamagotchi select blah from bonk where bletch smurf This will fail because a use query consumes rows only on demand so the MySQL server is still keeping information around about the first query when the second one comes in on the connection When you try the second query MySQL will throw an exception containing an obscure MySQL C API error message about commands out of sync This is not the only situation where this can happen but all of these issues boil down to the fact that MySQL requires that certain operations complete before you can start a new one The Result object must outlive the use of any Row objects it returns This is because the Row objects refer back to the Result object that created them for certain data Field names for example MySQL does this for efficiency because there is some information about a row that is the same for all rows in a result set We could avoid this in MySQL by making redundant copies
83. t endl return 1 Connection con use_exceptions try con connect IMG_DATABASE IMG_HOST IMG_USER IMG_PASSWORD Query query con query query lt lt SELECT FROM images WHERE id lt lt img_id ResUse res query use if res images img res fetch_row cout lt lt Content type image jpeg lt lt endl cout lt lt Content length lt lt img data length lt lt n n cout lt lt img data else cout lt lt Content type text plain lt lt endl lt lt endl cout lt lt ERROR No such image with ID lt lt img_id lt lt endl catch const BadQuery er Handle any query errors 41 MySQL User Manual cout lt lt Content type text plain lt lt endl lt lt endl cout lt lt QUERY ERROR lt lt er what lt lt endl return 1 catch const Exception amp er Catch all for any other MySQL exceptions cout lt lt Content type text plain lt lt endl lt lt endl cout lt lt GENERAL ERROR lt lt er what lt lt endl return 1 return 0 6 Using Unicode with MySQL 6 1 A Short History of Unicode with a focus on relevance to MySQL In the old days computer operating systems only dealt with 8 bit character sets That only allows for 256 possible characters but the modern Western languages have more charact
84. t endl Get each row in result set and print its contents mysqlpp Row row mysqlpp Row size_type i for i 0 row res at i i cout lt lt setw 20 lt lt row item lt lt lt lt setw 9 lt lt row num lt lt lt lt setw 9 lt lt row weight lt lt lt lt setw 9 lt lt row price lt lt lt lt setw 9 lt lt row sdate lt lt endl else cerr lt lt Failed to get stock table lt lt query error lt lt endl return 1 return 0 The main point of this example is that we re accessing fields in the row objects by name instead of index This is slower but obviously clearer We re also printing out the entire table not just one column 3 4 Exceptions By default MySQL uses exceptions to signal errors Most of the examples have a full set of exception handlers This is worthy of emulation All of MySQL s custom exceptions derive from a common base class Exception That in turn derives from Standard C s std exception class Since the library can indirectly cause exceptions to come from the Standard C Library it s possible to catch all exceptions from MySQL by just catching std exception by reference However it s better to have individual catch blocks for each of the concrete exception types that you expect and add a handler for either Exception or std exception to act as a catch all for unexpected exceptio
85. t lt Error lt lt er what lt lt endl return 1 return 0 Notice that we used the escape manipulator when building the INSERT query above This is because we re not using one of the MySQL types that does automatic escaping and quoting Serving images from BLOB column via CGI This example is also a very short one considering the function that it performs It retreives data loaded by load_jpeg and prints it out in the form a web server can accept for a CGI call This is examples cgi_jpeg cpp include lt mysql h gt include lt custom h gt 26 MySQL User Manual using namespace std using namespace mysqlpp define IMG_DATABASE mysql_cpp_data define IMG_HOST localhost define IMG_USER root define IMG_PASSWORD nunyabinness sql_create_2 images Ep 2y mysqlpp sql_int_unsigned id mysqlpp sql_blob data int main unsigned int img_id 0 char cgi_query getenv QUERY_STRING if cgi_query if strlen cgi_query lt 4 memcmp cgi_query id 3 cout lt lt Content type text plain lt lt endl lt lt endl cout lt lt ERROR Bad query string lt lt endl return 1 else img_id atoi cgi_query 3 else cerr lt lt Put this program into a web server s cgi bin directory then lt lt endl cerr lt lt invoke it with a URL like this lt lt endl cerr lt lt en
86. t lt er what lt lt endl return 1 Hd ct return 0 You install this in a web server s CGI program directory usually called cgi bin then call it with a URL like http my server com cgi bin cgi_jpeg id 1 That retrieves the JPEG with ID 1 from the table and returns it to the web server which will send it on to the browser 4 Template Queries Another powerful feature of MySQL is being able to set up template queries These are kind of like C s printf facility you give MySQL a string containing the fixed parts of the query and placeholders for the variable parts and you can later substitute in values into those placeholders The following program demonstrates how to use this feature This is examples tquery cpp include util h include lt iostream gt using namespace std int main int argc char argv try Establish the connection to the database server mysqlpp Connection con mysqlpp use_exceptions if connect_to_db argc argv con return 1 28 MySQL User Manual Build a template query to retrieve a stock item given by item name mysqlpp Query query con query query lt lt select from stock where item 0q query parse Retrieve an item added by resetdb it won t be there if tquery or custom3 is run since resetdb mysqlpp Result resl query store Nurnberger Brats if resl empty thro
87. t all the notices that refer to this License and to the absence of any warranty and distribute a copy of this License along with the Library You may charge a fee for the physical act of transferring a copy and you may at your option offer warranty protection in exchange for a fee 51 MySQL User Manual 2 You may modify your copy or copies of the Library or any portion of it thus forming a work based on the Library and copy and distribute such modifications or work under the terms of Section 1 above provided that you also meet all of these conditions a The modified work must itself be a software library b You must cause the files modified to carry prominent notices stating that you changed the files and the date of any change c You must cause the whole of the work to be licensed at no charge to all third parties under the terms of this License d If a facility in the modified Library refers to a function or a table of data to be supplied by an application program that uses the facility other than as an argument passed when the facility is invoked then you must make a good faith effort to ensure that in the event an application does not supply such function or table the facility still operates and performs whatever part of its purpose remains meaningful For example a function in a library to compute square roots has a purpose that is entirely well defined independent of the application Therefore Subsection 2d
88. the name and the second one won t be processed 4 2 Setting the Parameters at Execution Time To specify the parameters when you want to execute a query simply use Query store const SQLString amp parm0 const SQLString amp parm11 This type of multiple overload also exists for Query storein Query use and Query execute parm0 corresponds to the first parameter etc You may specify up to 25 parameters For example Result res query store Dinner Rolls item item price with the template query provided above would produce 30 MySQL User Manual select item price from stock where item Dinner Rolls The reason we didn t put the template parameters in numeric order select 30 fieldl 1 field2 from stock where 2 wheref 3q what will become apparent shortly 4 3 Parameter Types and Function Overloads There are quite a few overloads for each of Query s query execution functions store use execute It s possible to have code that looks like it should work but which doesn t because it s calling the wrong overload For instance query storein my_vector 1 query storein my_vector 1 The first one works and the second does not The cause is a vestigial second parameter to one of storein s overloads that s compatible with integers Being vestigial it s only getting in the way right now but we can t fix it until the next major version of the lib
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91. u under this License will not have their licenses terminated so long as such parties remain in full compliance 9 You are not required to accept this License since you have not signed it However nothing else grants you permission to modify or distribute the Library or its derivative works These actions are prohibited by law if you do not accept this License Therefore by modifying or distributing the Library or any work based on the Library you indicate your acceptance of this License to do so and all its terms and conditions for copying distributing or modifying the Library or works based on it 10 Each time you redistribute the Library or any work based on the Library the recipient automatically receives a license from the original licensor to copy distribute link with or modify the Library subject to these terms and conditions You may not impose any further restrictions on the recipients exercise of the rights granted herein You are not responsible for enforcing compliance by third parties with this License 11 If as a consequence of a court judgment or allegation of patent infringement or for any other reason not limited to patent issues conditions are imposed on you whether by court order agreement or otherwise that contradict the conditions of this License they do not excuse you from the conditions of this License If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other
92. uery classes now subclass from st ringst ream instead of the deprecated st rst ream v1 7 19 Fixed several const incorrectnesses in the Query classes v1 7 22 Removed reset query parameters from several Query class members This is not an API change because the parameters were given default values and the library would ignore any value other than the default So any program that tried to make them take another value wouldn t have worked anyway v1 7 24 Some freestanding functions didn t get moved into namespace mysqlpp when that namespace was created This release fixed that It doesn t affect the API if your program s C source files say using namespace mysqlpp within them v2 0 0 Removed Connection infoo I d call this an API change if I thought there were any programs out there actually using this Collapsed the Connection constructor taking a bool for setting the throw_exceptions flag and the default constructor into a single constructor using a default for the parameter Classes Connection and Query are now derived from the Lockable interface instead of implementing their own lock unlock functions In several instances functions that took objects by value now take them by const reference for efficiency Merged SOLQuery class s members into class Query Merged RowTemplate class s members into class Row 48 MySQL User Manual Reordered member variable declarations in some classes The most commo
93. umn Types In MySQL version 2 1 the new sql_types h header declares typedefs for all MySQL column types These typedefs all begin with sql_ and end with a lowercase version of the standard SQL type name For instance the MySQL typedef corresponding to TINYINT UNSIGNED is mysqlpp sql_tinyint_unsigned You do not have to use these typedef you could use an unsigned char here if you wanted to For that matter you could use a plain int in most cases MySQL is quite tolerant of this sort of thing The typedefs exist for style reasons for those who want their C code to use the closest equivalent type for any given SQL type Most of these typedefs use standard C data types but a few are aliases for a MySQL specific type For instance the SQL type DATETIME is mirrored in MySQL by mysqlpp DateTime For consistency sql1_types h includes a typedef alias for DateTime called mysqlpp sql_datetime 3 8 Handling SQL Nulls There is no equivalent of SQL s null in the standard C type system The primary distinction is one of type in SQL null is a column attribute which affects whether that column can hold a SQL null Just like the const keyword in the C type system this effectively doubles the number of SQL data types To emulate this MySQL provides the Null template to allow the creation of distinct nullable versions of existing C types So for example if you have a TINY INT UNSIGNED column that can have nulls the
94. usr share doc mysql devel but it can vary on different Linuxes Before you get started please read through any of the README files included with the MySQL distribution that are relevant to your platform We won t repeat all of that here Most of the examples require a test database created by reset db You run it like so exrun resetdb host user password port exrun is a Shell script that ensures that the MySQL example program you give as its first argument finds the correct shared library version If you run the example program directly it will search the system directories for the MySQL shared library That will only work correctly if you ve installed the library before running the examples You should run the examples before installing the library to ensure that the library is working correctly thus exrun See README examples for more details We ve been using POSIX file and path names for simplicity above but there s a Windows version of exrun called exrun bat It works the same way As for the remaining program arguments they are all optional but they must be in the order listed If you leave off the port number it uses the default value 3306 If you leave off the password it assumes you don t need one to log in If you leave off the user name it uses the name you used when logging on to the computer And if you leave off the host name it assumes the MySQL server is running on the local host A typi
95. w mysqlpp BadQuery UTF 8 bratwurst item not found in table run resetdb Replace the proper German name with a 7 bit ASCII approximation using a different template query query reset query lt lt update stock set item 0q where item 1q query parse mysqlpp ResNSel res2 query execute Nuerenberger Bratwurst resl at 0 at 0 c_str Print the new table contents print_stock_table query catch const mysqlpp BadQuery er Handle any query errors cerr lt lt Query error lt lt er what lt lt endl return 1 catch const mysqlpp BadConversiong er Handle bad conversions cerr lt lt Conversion error lt lt er what lt lt endl lt lt tretrieved data size lt lt er retrieved lt lt actual size lt lt er actual_size lt lt endl return 1 catch const mysqlpp Exceptiong er Catch all for any other MySQL exceptions cerr lt lt Error lt lt er what lt lt endl return 1 return 0 The line just before the call to query parse sets the template and the parse call puts it into effect From that point on you can re use this query by calling any of several Query member functions that accept query template parameters In this example we re using Query execute Let s dig into this feature a little deeper 4 1 Setting up Template Queries 29 MySQL U
96. you handle Unicode data depends on whether you re using the native Windows APL or the newer NET API First the native case Convert a C string in UTF 8 format to UCS 2 format void ToUCS2 LPTSTR pcOut int nOutLen const char kpcIn MultiByteToWideChar CP_UTF8 0 kpcIn 1 pcOut nOutLen Convert a UCS 2 string to C string in UTF 8 format void ToUTF8 char pcOut int nOutLen LPCWSTR kpcIn WideCharToMultiByte CP_UTF8 0 kpcIn 1 pcOut nOutLen 0 0 These functions leave out some important error checking so see examples vstudio mfc mfc_dlg cpp for the complete version If you re building a NET application such as perhaps because you re using Windows Forms it s better to use the NET libraries for this Convert a C string in UTF 8 format to a NET String in UCS 2 format String ToUCS2 const char utf8 return gcnew String utf8 0 strlen utf8 System Text ncoding UTF8 E Convert a NET String in UCS 2 format to a C string in UTF 8 format System Void ToUTF8 char pcOut int nOutLen String sIn 43 MySQL User Manual array lt Byte gt bytes System Text Encoding UTF8 gt GetBytes sIn nOutLen Math Min nOutLen 1 bytes gt Length System Runtime InteropServices Marshal Copy bytes 0 IntPtr pcOut nOutLen pcOut nOutLen 0 Unlike the native API versions these example

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