Wiley Professional C# 2005 with .NET 3.0
Contents
1. 1 1 Reference Type Interface Types Value Type Self describing Types Pointer Types User defined Value Types Built in Value Types Class Types Enumerations Boxed Value Delegates Types User defined Reference Types Figure 1 1 The following table explains the types shown in Figure 1 1 Type Meaning Type Base class that represents any type Value Type Base class that represents any value type Reference Types Any data types that are accessed through a reference and stored on the heap Built in Value Types Includes most of the standard primitive types which represent numbers Boolean values or characters Enumerations Sets of enumerated values User defined Value Types that have been defined in source code and are stored as value Types types In C terms this means any struct Continued 11 24727c01 qxd WroxPro 5 7 07 12 12 Part The CF Language PM Page 12 F Self describing Types Arrays Class Types Delegates User defined Reference Types Boxed Value Types Type Meaning Interface Types Interfaces Pointer Types Pointers Data types that provide information about themselves for the bene fit of the garbage collector see the next section Any type that contains an array of objects Types that are self describing but are not arrays Types that are designed to hold referenc2. Studio 2005 supplies Web Forms They allow you to build ASP NET pages graphically in the same way that Visual Basic 6 or C Builder windows are cre ated in other words by dragging controls from a toolbox onto a form then flipping over to the code aspect of that form and writing event handlers for the controls When you use C to create a Web Form you are creating a C class that inherits from the Page base class and an ASP NET page that designates that class as its code behind Of course you don t have to use C to create a Web Form you can use Visual Basic 2005 or another NET compliant language just as well In the past the difficulty of Web development discouraged some teams from attempting it To succeed in Web development you had to know so many different technologies such as VBScript ASP DHTML JavaScript and so on By applying the Form concepts to Web pages Web Forms have made Web devel opment considerably easier Web Server Controls The controls used to populate a Web Form are not controls in the same sense as ActiveX controls Rather they are XML tags in the ASP NET namespace that the Web browser dynamically transforms into HTML and client side script when a page is requested Amazingly the Web server is able to render the same server side control in different ways producing a transformation appropriate to the requestor s particu lar Web browser This means that it is now easy to write fairly sophisticated user interface
3. The C Language NET Framework Classes 20 Perhaps one of the biggest benefits of writing managed code at least from a developer s point of view is that you get to use the NET base class library The NET base classes are a massive collection of managed code classes that allow you to do almost any of the tasks that were previously available through the Windows API These classes follow the same object model IL uses based on single inheritance This means that you can either instantiate objects of whichever NET base class is appropriate or you can derive your own classes from them The great thing about the NET base classes is that they have been designed to be very intuitive and easy to use For example to start a thread you call the Start method of the Thread class To disable a TextBox you set the Enabled property of a TextBox object to false This approach while familiar to Visual Basic and Java developers whose respective libraries are just as easy to use will be a welcome relief to C developers who for years have had to cope with such API functions as GetDIBits RegisterWndClassEx and IsEqualIID as well as a whole plethora of functions that required Windows handles to be passed around On the other hand C developers always had easy access to the entire Windows API whereas Visual Basic 6 and Java developers were more restricted in terms of the basic operating system functionality that they have access t
4. for starters What technology should you use Well it really comes down to what you are trying to achieve as each technology is better used in a particular situation With that in mind Microsoft really brought all these technologies together and with the release of the NET Framework 3 0 you now have a single way to move data the Windows Communication Foundation WCF WCF provides you with the ability to build your service one time and then expose this service in a multitude of ways under different protocols even by just making changes within a configuration file You will find WCF a powerful new way of connecting disparate systems Chapter 40 Windows Communication Foundation covers this all in detail The Role of C in the NET Enterprise Architecture C requires the presence of the NET runtime and it will probably be a few years before most clients particularly most home computers have NET installed In the meantime installing a C application is likely to mean also installing the NET redistributable components Because of that it is likely that we will see many C applications first in the enterprise environment Indeed C arguably presents an outstanding opportunity for organizations that are interested in building robust n tiered client server applications When combined with ADO NET C has the ability to access quickly and generically data stores such as SQL Server and Oracle databases The returned datase
5. the primitive data types in the CTS discussed in Chapter 3 Objects and Types Q Windows GUI support and controls see Chapter 28 Windows Forms and 31 Windows Presentation Foundation Q Web Forms ASP NET discussed in Chapters 32 ASP NET Pages and 33 ASP NET Development A Data access ADO NET see Chapters 25 Data Access with NET 27 NET Programming with SQL Server 2005 and 26 Manipulating XML Q Directory access see Chapter 42 Directory Services 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 21 F Chapter 1 NET Architecture File system and registry access see Chapter 24 Manipulating Files and the Registry Networking and Web browsing see Chapter 35 Accessing the Internet NET attributes and reflection see Chapter 12 Reflection Oooo Access to aspects of the Windows OS environment variables and so on see Chapter 19 NET Security Q COM interoperability see Chapters 38 Enterprise Services and 23 COM Interoperability Incidentally according to Microsoft sources a large proportion of the NET base classes have actually been written in C Namespaces Namespaces are the way that NET avoids name clashes between classes They are designed to avoid the situation in which you define a class to represent a customer name your class Customer and then someone else does the same thing a likely scenario the prop
6. 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 1 F Part I The C Language Chapter 1 NET Architecture Chapter 2 C Basics Chapter 3 Objects and Types Chapter 4 Inheritance Chapter 5 Arrays Chapter 6 Operators and Casts Chapter 7 Delegates and Events Chapter 8 Strings and Regular Expressions Chapter 9 Generics Chapter 19 Collections Chapter 11 Memory Management and Pointers Chapter 12 Reflection Chapter 13 Errors and Exceptions 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 2 F 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 3 P NET Architecture Throughout this book we emphasize that the C language cannot be viewed in isolation but must be considered in parallel with the NET Framework The C compiler specifically targets NET which means that all code written in C will always run within the NET Framework This has two important consequences for the C language Q The architecture and methodologies of C reflect the underlying methodologies of NET A In many cases specific language features of C actually depend upon features of NET or of the NET base classes Because of this dependence it is important to gain some understanding of the architecture and methodology of NET before you begin C programming That is the purpose of this chapter This chapter begins by going over what happens when all code including C that targets NET is compiled and run Once you have this broad overvie
7. 5 can Scripting Languages Scripting languages are still around although in general their importance is likely to decline with the advent of NET JScript on the other hand has been upgraded to JScript NET You can now write ASP NET pages in JScript NET run JScript NET as a compiled rather than an interpreted language and write strongly typed JScript NET code With ASP NET there is no reason to use scripting languages in server side Web pages VBA is however still used as a language for Microsoft Office and Visual Studio macros COM and COM Technically speaking COM and COM aren t technologies targeted at NET because components based on them cannot be compiled into IL although it s possible to do so to some degree using managed C if the original COM component was written in C However COM remains an important tool because its features are not duplicated in NET Also COM components will still work and NET incorporates COM interoperability features that make it possible for managed code to call up COM components and vice versa this is discussed in Chapter 23 COM Interoperability In general however you will prob ably find it more convenient for most purposes to code new components as NET components so that you can take advantage of the NET base classes as well as the other benefits of running as managed code A Closer Look at Intermediate Language From what you learned in the previous section Microso
8. 7 F Chapter 1 NET Architecture The compiler raises an error if you attempt to use features that are not supported by NET on managed types for example templates or multiple inheritance of classes You will also find that you will need to use nonstandard C features such as the _gc keyword shown in the previous code when using managed classes Because of the freedom that C allows in terms of low level pointer manipulation and so on the C compiler is not able to generate code that will pass the CLR s memory type safety tests If it s important that your code be recognized by the CLR as memory type safe you ll need to write your source code in some other language such as C or Visual Basic 2005 Visual J 2005 The latest language to be added to the mix is Visual J 2005 Prior to NET Framework 1 1 users were able to use J only after making a separate download Now the J language is built into the NET Framework Because of this J users are able to take advantage of all the usual features of Visual Studio 2005 Microsoft expects that most J users will find it easiest to use J if they want to work with NET Instead of being targeted at the Java runtime libraries J uses the same base class libraries that the rest of the NET compliant languages use This means that you can use J for building ASP NET Web applications Windows Forms XML Web services and everything else that is possible just as C and Visual Basic 200
9. age instances of reference types are always stored in an area of memory known as the managed heap whereas value types are normally stored on the stack although if value types are declared as fields within reference types they will be stored inline on the heap Chapter 2 CH Basics discusses the stack and the heap and how they work Strong Data Typing One very important aspect of IL is that itis based on exceptionally strong data typing That means that all variables are clearly marked as being of a particular specific data type there is no room in IL for example for the Variant data type recognized by Visual Basic and scripting languages In particular IL does not normally permit any operations that result in ambiguous data types For instance Visual Basic 6 developers are used to being able to pass variables around without worrying too much about their types because Visual Basic 6 automatically performs type conversion C devel opers are used to routinely casting pointers between different types Being able to perform this kind of operation can be great for performance but it breaks type safety Hence it is permitted only under certain 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 10 F Part The CF Language circumstances in some of the languages that compile to managed code Indeed pointers as opposed to references are permitted only in marked blocks of code in C and not at all in Visual Basic although they are allow
10. all up code in a given assembly do not need to refer to the registry or to any other data source in order to find out how to use that assembly This is a significant break from the old COM way of doing things in which the GUIDs of the components and interfaces had to be obtained from the registry and in some cases the details of the methods and properties exposed would need to be read from a type library Having data spread out in up to three different locations meant there was the obvious risk of something getting out of synchronization which would prevent other software from being able to use the compo nent successfully With assemblies there is no risk of this happening because all the metadata is stored with the program executable instructions Note that even though assemblies are stored across several files there are still no problems with data going out of synchronization This is because the file that contains the assembly entry point also stores details of and a hash of the contents of the other files which means that if one of the files gets replaced or in any way tampered with this will almost certainly be detected and the assembly will refuse to load Assemblies come in two types shared and private assemblies Private Assemblies Private assemblies are the simplest type They normally ship with software and are intended to be used only with that software The usual scenario in which you will ship private assemblies is when you
11. are supplying an application in the form of an executable and a number of libraries where the libraries con tain code that should only be used with that application The system guarantees that private assemblies will not be used by other software because an application may only load private assemblies that are located in the same folder that the main executable is loaded in or in a subfolder of it Because you would normally expect that commercial software would always be installed in its own directory this means that there is no risk of one software package overwriting modifying or accidentally loading private assemblies intended for another package Because private assemblies can be used only by the software package that they are intended for this means that you have much more control over 18 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 19 F Chapter 1 NET Architecture what software uses them There is therefore less need to take security precautions because there is no risk for example of some other commercial software overwriting one of your assemblies with some new version of it apart from the case where software is designed specifically to perform malicious damage There are also no problems with name collisions If classes in your private assembly happen to have the same name as classes in someone else s private assembly that doesn t matter because any given applica tion will only be able to see the one set of p
12. arget NET including C You also learned how the strongly typed nature of IL enables language interoperability as well as CLR services such as garbage collection and security Finally you learned how C can be used as the basis for applications that are built on several NET tech nologies including ASP NET Chapter 2 discusses how to write code in C 28
13. asier because different versions of the same component can run side by side on the same machine without conflicting Q Your ASP NET code won t look like spaghetti code Q You can leverage a lot of the functionality in the NET base classes Q For applications requiring a Windows Forms user interface C makes it very easy to write this kind of application Windows Forms have to some extent been downplayed in the past year due to the advent of Web Forms and Internet based applications However if you or your colleagues lack expertise in JavaScript ASP or related technologies Windows Forms are still a viable option for creating a user interface with speed and ease Just remember to factor your code so that the user interface logic is separate from the business logic and the data access code Doing so will allow you to migrate your application to the browser at some point in the future if you need to do so Also it is likely that Windows Forms will remain the dom inant user interface for applications for use in homes and small businesses for a long time to come In addition to this the new smart client features of Windows Forms the ability to easily work in an online offline mode will bring a new round of exciting applications Summary 26 This chapter has covered a lot of ground briefly reviewing important aspects of the NET Framework and C s relationship to it It started by discussing how all languages that target NET are compil
14. d as narrowly or as widely as you want The exception architecture ensures that when an error condition occurs execution can immediately jump to the exception handler routine that is most specifically geared to handle the exception condition in question The architecture of exception handling also provides a convenient means to pass an object containing precise details of the exception condition to an exception handling routine This object might include an appropriate message for the user and details of exactly where in the code the exception was detected Most exception handling architecture including the control of program flow when an exception occurs is handled by the high level languages C Visual Basic 2005 C and is not supported by any special IL commands C for example handles exceptions using try catch and finally blocks of code For more details see Chapter 13 What NET does do however is provide the infrastructure to allow compilers that target NET to support exception handling In particular it provides a set of NET classes that can represent the exceptions and the language interoperability to allow the thrown exception objects to be interpreted by the exception handling code irrespective of what language the exception handling code is written in This language independence is absent from both the C and Java implementations of exception handling although it is present to a limited extent in the COM mechani
15. e in advance what security permissions it will require to run The importance of code based security is that it reduces the risks associated with running code of dubious origin such as code that you ve downloaded from the Internet For example even if code is running under the administrator account it is possible to use code based security to indicate that that code should still not be permitted to perform certain types of operation that the administrator account would nor mally be allowed to do such as read or write to environment variables read or write to the registry or access the NET reflection features Security issues are covered in more depth in Chapter 19 NET Security Application Domains 14 Application domains are an important innovation in NET and are designed to ease the overhead involved when running applications that need to be isolated from each other but that also need to be able to communicate with each other The classic example of this is a Web server application which may be simultaneously responding to a number of browser requests It will therefore probably have a num ber of instances of the component responsible for servicing those requests running simultaneously In pre NET days the choice would be between allowing those instances to share a process with the resultant risk of a problem in one running instance bringing the whole Web site down or isolating those instances in separate processes w
16. ed in great detail in this chapter because they are covered in detail in Chapter 16 Assemblies but we summarize the main points here 17 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 18 F Part The CF Language An assembly is completely self describing and is a logical rather than a physical unit which means that it can be stored across more than one file indeed dynamic assemblies are stored in memory not on file at all If an assembly is stored in more than one file there will be one main file that contains the entry point and describes the other files in the assembly Note that the same assembly structure is used for both executable code and library code The only real difference is that an executable assembly contains a main program entry point whereas a library assembly doesn t An important characteristic of assemblies is that they contain metadata that describes the types and methods defined in the corresponding code An assembly however also contains assembly metadata that describes the assembly itself This assembly metadata contained in an area known as the manifest allows checks to be made on the version of the assembly and on its integrity ildasm a Windows based utility can be used to inspect the contents of an assembly including the man ifest and metadata ildasm is discussed in Chapter 16 Assemblies The fact that an assembly contains program metadata means that applications or other assemblies that c
17. ed in managed C Using pointers in your code causes it to fail the memory type safety checks performed by the CLR You should note that some languages compatible with NET such as Visual Basic 2005 still allow some laxity in typing but that is only possible because the compilers behind the scenes ensure that the type safety is enforced in the emitted IL Although enforcing type safety might initially appear to hurt performance in many cases the benefits gained from the services provided by NET that rely on type safety far outweigh this performance loss Such services include Language interoperability Garbage collection Security 1 1 0 E Application domains The following sections take a closer look at why strong data typing is particularly important for these features of NET The Importance of Strong Data Typing for Language Interoperability If a class is to derive from or contains instances of other classes it needs to know about all the data types used by the other classes This is why strong data typing is so important Indeed it is the absence of any agreed on system for specifying this information in the past that has always been the real barrier to inheri tance and interoperability across languages This kind of information is simply not present in a standard executable file or DLL Suppose that one of the methods of a Visual Basic 2005 class is defined to return an Integer one of the standard data types avai
18. ed into Microsoft Intermediate Language IL before this is compiled and executed by the Common Language 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 27 F Chapter 1 NET Architecture Runtime CLR This chapter also discussed the roles of the following features of NET in the compilation and execution process Q Assemblies and NET base classes Q COM components Q JIT compilation Q Application domains Q Garbage collection Figure 1 4 provides an overview of how these features come into play during compilation and execution C Source VB NET Code Source Code COMPILATION Language ASSEMBLY Interoperability ASSEMBLY containing IL t gt gt containing IL CODE through CTS CODE and CLS NET base classes Y gt CLR ORGANIZES Assemblies loaded m JIT compilation Security permissions granted EXECUTION Memory type safety checked Creates App PROCESS Domain Application domain gt Garbage collector cleans up sources CODE EXECUTES HERE a COM interop services legacy COM component Figure 1 4 27 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 28 F Part The CF Language You learned about the characteristics of IL particularly its strong data typing and object orientation and how these characteristics influence the languages that t
19. es a utility that creates a wrapper for ActiveX controls so that they can be placed on Windows Forms As is the case with Web Controls Windows Control creation involves deriving from a particular class System Windows Forms Control Windows Services 24 A Windows Service originally called an NT Service is a program designed to run in the background in Windows NT 2000 XP 2003 but not Windows 9x Services are useful where you want a program to be running continuously and ready to respond to events without having been explicitly started by the user A good example is the World Wide Web Service on Web servers which listens for Web requests from clients 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 25 F Chapter 1 NET Architecture It is very easy to write services in C NET Framework base classes are available in the System ServiceProcess namespace that handle many of the boilerplate tasks associated with services and in addition Visual Studio NET allows you to create a C Windows Service project which uses C source code for a basic Windows service Chapter 22 Windows Services explores how to write C Windows Services Windows Communication Foundation WCF Looking at how you move data and services from one point to another using Microsoft based technolo gies you will find that there are a lot of choices at your disposal For instance you can use ASP NET Web services NET Remoting Enterprise Services and MSMQ
20. es to methods Types that have been defined in source code and are stored as refer ence types In C terms this means any class A value type that is temporarily wrapped in a reference so that it can be stored on the heap We won t list all of the built in value types here because they are covered in detail in Chapter 3 Objects and Types In C each predefined type recognized by the compiler maps onto one of the IL built in types The same is true in Visual Basic 2005 Common Language Specification 12 The Common Language Specification CLS works with the CTS to ensure language interoperability The CLS is a set of minimum standards that all compilers targeting NET must support Because IL is a very rich language writers of most compilers will prefer to restrict the capabilities of a given compiler to only support a subset of the facilities offered by IL and the CTS That is fine as long as the compiler supports everything that is defined in the CLS It is perfectly acceptable to write non CLS compliant code However if you do the compiled IL code isn t guaranteed to be fully language interoperable For example take case sensitivity IL is case sensitive Developers who work with case sensitive languages regularly take advantage of the flexibility that this case sensitivity gives them when selecting variable names Visual Basic 2005 however is not case sensitive The CLS works around this by indicating tha
21. ft Intermediate Language obviously plays a fun damental role in the NET Framework As C developers we now understand that our C code will be compiled into IL before it is executed indeed the C compiler only compiles to managed code It makes sense then to now take a closer look at the main characteristics of IL because any language that targets NET will logically need to support the main characteristics of IL too 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 8 F Part The CF Language Here are the important features of IL Object orientation and use of interfaces Strong distinction between value and reference types Strong data typing Error handling through the use of exceptions COocoo do Use of attributes The following sections take a closer look at each of these characteristics Support for Object Orientation and Interfaces The language independence of NET does have some practical limitations IL is inevitably going to implement some particular programming methodology which means that languages targeting it are going to have to be compatible with that methodology The particular route that Microsoft has chosen to follow for IL is that of classic object oriented programming with single implementation inheritance of classes If you are unfamiliar with the concepts of object orientation refer to Appendix A for more information Appendix A is posted at www wrox com In addition to classic object oriented programmin
22. g IL also brings in the idea of interfaces which saw their first implementation under Windows with COM NET interfaces are not the same as COM interfaces they do not need to support any of the COM infrastructure for example they are not derived from IUnknown and they do not have associated globally unique identifiers more commonly know as GUIDs However they do share with COM interfaces the idea that they provide a contract and classes that implement a given interface must provide implementations of the methods and properties specified by that interface You have now seen that working with NET means compiling to IL and that in turn means that you will need to use traditional object oriented methodologies However that alone is not sufficient to give you language interoperability After all C and Java both use the same object oriented paradigms but they are still not regarded as interoperable We need to look a little more closely at the concept of language interoperability To start with we need to consider exactly what we mean by language interoperability After all COM allowed components written in different languages to work together in the sense of calling each other s methods What was inadequate about that COM by virtue of being a binary standard did allow com ponents to instantiate other components and call methods or properties against them without worrying about the language the respective components were written in In
23. ith the associated performance overhead Up until now the only means of isolating code has been through processes When you start a new appli cation it runs within the context of a process Windows isolates processes from each other through address 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 15 F Chapter 1 NET Architecture spaces The idea is that each process has available 4GB of virtual memory in which to store its data and executable code 4GB is for 32 bit systems 64 bit systems use more memory Windows imposes an extra level of indirection by which this virtual memory maps into a particular area of actual physical memory or disk space Each process gets a different mapping with no overlap between the actual physical mem ories that the blocks of virtual address space map to see Figure 1 2 Physical Memory PROCESS 1 Physical memory or disk space 4GB virtual memory PROCESS 2 Physical memory or disk space 4GB virtual memory Figure 1 2 In general any process is able to access memory only by specifying an address in virtual memory processes do not have direct access to physical memory Hence it is simply impossible for one process to access the memory allocated to another process This provides an excellent guarantee that any badly behaved code will not be able to damage anything outside its own address space Note that on Windows 95 98 these safeguards are not quite as thorough a
24. ken On a related note C and NET will probably influence the way you physically package your reusable classes In the past many developers crammed a multitude of classes into a single physical component because this arrangement made deployment a lot easier if there was a versioning problem you knew just where to look Because deploying NET enterprise components involves simply copying files into directories developers can now package their classes into more logical discrete components without encountering DLL Hell Last but not least ASP NET pages coded in C constitute an excellent medium for user interfaces Because ASP NET pages compile they execute quickly Because they can be debugged in the Visual Studio 2005 IDE they are robust Because they support full scale language features such as early binding inheritance and modularization ASP NET pages coded in C are tidy and easily maintained Seasoned developers acquire a healthy skepticism about strongly hyped new technologies and languages and are reluctant to utilize new platforms simply because they are urged to If you re an enterprise devel oper in an IT department though or if you provide application services across the World Wide Web let us assure you that C and NET offer at least four solid benefits even if some of the more exotic features like XML Web services and server side controls don t pan out Q Component conflicts will become infrequent and deployment is e
25. lable in Visual Basic 2005 C simply does not have any data type of that name Clearly you will only be able to derive from the class use this method and use the return type from C code if the compiler knows how to map Visual Basic 2005 s Integer type to some known type that is defined in C So how is this problem circumvented in NET Common Type System This data type problem is solved in NET through the use of the Common Type System CTS The CTS defines the predefined data types that are available in IL so that all languages that target the NET Framework will produce compiled code that is ultimately based on these types For the previous example Visual Basic 2005 s Integer is actually a 32 bit signed integer which maps exactly to the IL type known as Int32 This will therefore be the data type specified in the IL code Because the C compiler is aware of this type there is no problem At source code level C refers to Int32 with the keyword int so the compiler will simply treat the Visual Basic 2005 method as if it returned an int 10 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 11 F Chapter 1 NET Architecture The CTS doesn t specify merely primitive data types but a rich hierarchy of types which includes well defined points in the hierarchy at which code is permitted to define its own types The hierarchical struc ture of the CTS reflects the single inheritance object oriented methodology of IL and resembles Figure
26. loper most of the background code is not available as source code Not only that it does not support implementation inheritance and the standard data types Visual Basic 6 uses are incompatible with NET Visual Basic 6 was upgraded to Visual Basic NET in 2002 and the changes that were made to the lan guage are so extensive you might as well regard Visual Basic as a new language Existing Visual Basic 6 code does not compile to the present Visual Basic 2005 code or to Visual Basic NET 2002 and 2003 for that matter Converting a Visual Basic 6 program to Visual Basic 2005 requires extensive changes to the code However Visual Studio 2005 the upgrade of Visual Studio for use with NET can do most of the changes for you If you attempt to read a Visual Basic 6 project into Visual Studio 2005 it will upgrade the project for you which means that it will rewrite the Visual Basic 6 source code into Visual Basic 2005 source code Although this means that the work involved for you is heavily cut down you will need to check through the new Visual Basic 2005 code to make sure that the project still works as intended because the conversion might not be perfect One side effect of this language upgrade is that itis no longer possible to compile Visual Basic 2005 to native executable code Visual Basic 2005 compiles only to IL just as C does If you need to continue coding in Visual Basic 6 you can do so but the executable code produced will complete
27. low every component call with a check to Err Number to make sure that the call had gone well ASP NET is a complete revision of ASP that fixes many of its problems It does not replace ASP rather ASP NET pages can live side by side on the same server with legacy ASP applications Of course you can also program ASP NET with C The following section explores the key features of ASP NET For more details refer to Chapters 32 ASP NET Pages and 33 ASP NET Development Features of ASPNET 22 First and perhaps most important ASP NET pages are structured That is each page is effectively a class that inherits from the NET System Web UI Page class and can override a set of methods that are evoked during the Page object s lifetime You can think of these events as page specific cousins of the OnApplication_Start and OnSession_Start events that went in the global asa files of plain old ASP Because you can factor a page s functionality into event handlers with explicit meanings ASP NET pages are easier to understand Another nice thing about ASP NET pages is that you can create them in Visual Studio 2005 the same environment in which you create the business logic and data access components that those ASP NET pages use A Visual Studio 2005 project or solution contains all of the files associated with an application Moreover you can debug your classic ASP pages in the editor as well in the old days of Visual InterDev i
28. ly ignore the NET Framework and you ll need to keep Visual Studio 6 installed if you want to continue to work in this developer environment Visual C 2005 Visual C 6 already had a large number of Microsoft specific extensions on Windows With Visual C NET extensions have been added to support the NET Framework This means that existing C source code will continue to compile to native executable code without modification It also means however that it will run independently of the NET runtime If you want your C code to run within the NET Framework you can simply add the following line to the beginning of your code using lt mscorlib dl1 gt You can also pass the flag c1r to the compiler which then assumes that you want to compile to managed code and will hence emit IL instead of native machine code The interesting thing about C is that when you compile to managed code the compiler can emit IL that contains an embedded native executable This means that you can mix managed types and unmanaged types in your C code Thus the managed C code class MyClass defines a plain C class whereas the code _ gc class MyClass will give you a managed class just as if you d written the class in C or Visual Basic 2005 The advantage of using managed C over C code is that you can call unmanaged C classes from managed C code without having to resort to COM interop 24727c01 qxd WroxPro 5 7 07 12 12 PM Page
29. ly takes one client not to do so and the object sits in memory In some ways this is a potentially more serious problem than a simple C style memory leak because the COM object may exist in its own process which means that it will never be removed by the system at least with C memory leaks the system can reclaim all memory when the process terminates The NET runtime relies on the garbage collector instead This is a program whose purpose is to clean up memory The idea is that all dynamically requested memory is allocated on the heap that is true for all languages although in the case of NET the CLR maintains its own managed heap for NET applications to use Every so often when NET detects that the managed heap for a given process is becoming full and therefore needs tidying up it calls the garbage collector The garbage collector runs through variables currently in scope in your code examining references to objects stored on the heap to identify which ones are accessible from your code that is to say which objects have references that refer to them Any 13 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 14 F Part The CF Language objects that are not referred to are deemed to be no longer accessible from your code and can therefore be removed Java uses a system of garbage collection similar to this Garbage collection works in NET because IL has been designed to facilitate the process The principle requires that you cann
30. n used on the Windows platform for deallocating memory that processes have dynamically requested from the system Make the application code do it all manually Q Make objects maintain reference counts Having the application code responsible for deallocating memory is the technique used by lower level high performance languages such as C It is efficient and it has the advantage that in general resources are never occupied for longer than necessary The big disadvantage however is the frequency of bugs Code that requests memory also should explicitly inform the system when it no longer requires that memory However itis easy to overlook this resulting in memory leaks Although modern developer environments do provide tools to assist in detecting memory leaks they remain difficult bugs to track down because they have no effect until so much memory has been leaked that Windows refuses to grant any more to the process By this point the entire computer may have appreciably slowed down due to the memory demands being made on it Maintaining reference counts is favored in COM The idea is that each COM component maintains a count of how many clients are currently maintaining references to it When this count falls to zero the component can destroy itself and free up associated memory and resources The problem with this is that it still relies on the good behavior of clients to notify the component that they have finished with it It on
31. nit testing class libraries and for creating Unix or Linux daemon processes However more often you ll use C to create applications that use many of the tech nologies associated with NET This section gives you an overview of the different types of applications that you can write in C 21 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 22 F Part The CF Language Creating ASP NET Applications Active Server Pages ASP is a Microsoft technology for creating Web pages with dynamic content An ASP page is basically an HTML file with embedded chunks of server side VBScript or JavaScript When a client browser requests an ASP page the Web server delivers the HTML portions of the page process ing the server side scripts as it comes to them Often these scripts query a database for data and mark up that data in HTML ASP is an easy way for clients to build browser based applications However ASP is not without its shortcomings First ASP pages sometimes render slowly because the server side code is interpreted instead of compiled Second ASP files can be difficult to maintain because they were unstructured the server side ASP code and plain HTML are all jumbled up together Third ASP sometimes makes development difficult because there is little support for error handling and type checking Specifically if you are using VBScript and want to implement error handling in your pages you have to use the On Error Resume Next statement and fol
32. nt it is not itself part of NET Some features are supported by NET but not by C and you might be surprised to learn that some features of the C language are not supported by NET for example some instances of operator overloading However because the C language is intended for use with NET it is important for you to have an understanding of this Framework if you want to develop applications in C effectively So this chapter takes some time to peek underneath the surface of NET Let s get started The Common Language Runtime Central to the NET Framework is its runtime execution environment known as the Common Language Runtime CLR or the NET runtime Code running under the control of the CLR is often termed managed code However before it can be executed by the CLR any source code that you develop in C or some other language needs to be compiled Compilation occurs in two steps in NET 1 Compilation of source code to IL 2 Compilation of IL to platform specific code by the CLR This two stage compilation process is very important because the existence of the IL managed code is the key to providing many of the benefits of NET Advantages of Managed Code Microsoft Intermediate Language shares with Java byte code the idea that it is a low level language with a simple syntax based on numeric codes rather than text which can be very quickly translated into native machine code Having this well defined universal
33. o from their respective languages What is new about the NET base classes is that they combine the ease of use that was typical of the Visual Basic and Java libraries with the relatively com prehensive coverage of the Windows API functions Many features of Windows still are not available through the base classes and for those you will need to call into the API functions but in general these are now confined to the more exotic features For everyday use you will probably find the base classes adequate And if you do need to call into an API function NET offers a so called platform invoke that ensures data types are correctly converted so the task is no harder than calling the function directly from C code would have been regardless of whether you are coding in C C or Visual Basic 2005 WinCV a Windows based utility can be used to browse the classes structs interfaces and enums in the base class library WinCV is discussed in Chapter 14 Visual Studio 2005 Although Chapter 3 is nominally dedicated to the subject of base classes in reality once we have com pleted our coverage of the syntax of the C language most of the rest of this book shows you how to use various classes within the NET base class library for both NET 2 0 and the new NET Framework 3 0 That is how comprehensive base classes are As a rough guide the areas covered by the NET 2 0 and 3 0 base classes include Q Core features provided by IL including
34. ociated with passing data between processes The idea is that any one process is 15 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 16 F Part I The CF Language divided into a number of application domains Each application domain roughly corresponds to a single application and each thread of execution will be running in a particular application domain see Figure 1 3 PROCESS 4GB virtual memory APPLICATION DOMAIN an application uses some of this virtual memory APPLICATION DOMAIN another application uses some of this virtual memory Figure 1 3 If different executables are running in the same process space they are clearly able to easily share data because theoretically they can directly see each other s data However although this is possible in principle the CLR makes sure that this does not happen in practice by inspecting the code for each running appli cation to ensure that the code cannot stray outside its own data areas This looks at first sight like an almost impossible trick to pull off after all how can you tell what the program is going to do without actually running it In fact itis usually possible to do this because of the strong type safety of the IL In most cases unless code is using unsafe features such as pointers the data types it is using will ensure that memory is not accessed inappropriately For example NET array types perform bounds checking to ensure that no
35. ode will run on beyond basic generalities such as that it will be an x86 compatible processor or an Alpha processor Visual Studio 6 for example optimizes for a generic Pentium machine so the code that it generates cannot take advantage of hardware features of Pentium III processors On the other hand the JIT compiler can do all the optimizations that Visual Studio 6 can and in addition it will optimize for the particular processor that the code is running on Language Interoperability The use of IL not only enables platform independence it also facilitates language interoperability Simply put you can compile to IL from one language and this compiled code should then be interoperable with code that has been compiled to IL from another language You re probably now wondering which languages aside from C are interoperable with NET so the fol lowing sections briefly discuss how some of the other common languages fit into NET Visual Basic 2005 Visual Basic NET 2002 underwent a complete revamp from Visual Basic 6 to bring it up to date with the first version of the NET Framework The Visual Basic language itself had dramatically evolved from VB6 and this meant that VB6 was not a suitable language for running NET programs For example VB6 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 6 F Part The CF Language is heavily integrated into Component Object Model COM and works by exposing only event handlers as source code to the deve
36. order to achieve this however each object had to be instantiated through the COM runtime and accessed through an interface Depending on the threading models of the relative components there may have been large performance losses associated with marshaling data between apartments or running components or both on different threads In the extreme case of components hosted as an executable rather than DLL files separate processes would need to be created in order to run them The emphasis was very much that compo nents could talk to each other but only via the COM runtime In no way with COM did components written in different languages directly communicate with each other or instantiate instances of each other it was always done with COM as an intermediary Not only that but the COM architecture 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 9 F Chapter 1 NET Architecture did not permit implementation inheritance which meant that it lost many of the advantages of object oriented programming An associated problem was that when debugging you would still have to debug components written in different languages independently It was not possible to step between languages in the debugger So what we really mean by language interoperability is that classes written in one language should be able to talk directly to classes written in another language In particular A Aclass written in one language can inherit from a class written in ano
37. ortion of businesses that have customers seems to be quite high A namespace is no more than a grouping of data types but it has the effect that the names of all data types within a namespace are automatically prefixed with the name of the namespace It is also possible to nest namespaces within each other For example most of the general purpose NET base classes are in a namespace called System The base class Array is in this namespace so its full name is System Array NET requires all types to be defined in a namespace for example you could place your Customer class in a namespace called YourCompanyName This class would have the full name YourCompanyName Customer Ifa namespace is not explicitly supplied the type will be added to a nameless global namespace Microsoft recommends that for most purposes you supply at least two nested namespace names the first one refers to the name of your company and the second one refers to the name of the technology or software package that the class is a member of such as YourCompanyName SalesServices Customer This protects in most situations the classes in your application from possible name clashes with classes written by other organizations Chapter 2 C Basics looks more closely at namespaces Creating NET Applications Using C C can also be used to create console applications text only applications that run in a DOS window You ll probably use console applications when u
38. ot get references to existing objects other than by copying existing references and that IL be type safe In this context what we mean is that if any reference to an object exists then there is sufficient information in the reference to exactly determine the type of the object It would not be possible to use the garbage collection mechanism with a language such as unmanaged C for example because C allows pointers to be freely cast between types One important aspect of garbage collection is that it is not deterministic In other words you cannot guarantee when the garbage collector will be called it will be called when the CLR decides that it is needed unless you explicitly call the collector though it is also possible to override this process and call up the garbage collector in your code Security NET can really excel in terms of complementing the security mechanisms provided by Windows because it can offer code based security whereas Windows only really offers role based security Role based security is based on the identity of the account under which the process is running that is who owns and is running the process Code based security on the other hand is based on what the code actu ally does and on how much the code is trusted Thanks to the strong type safety of IL the CLR is able to inspect code before running it in order to determine required security permissions NET also offers a mechanism by which code can indicat
39. out of bounds array operations are permitted If a running application does need to communicate or share data with other applications running in different application domains it must do so by calling on NET s remoting services Code that has been verified to check that it cannot access data outside its application domain other than through the explicit remoting mechanism is said to be memory type safe Such code can safely be run along side other type safe code in different application domains within the same process Error Handling with Exceptions The NET Framework is designed to facilitate handling of error conditions using the same mechanism based on exceptions that is employed by Java and C C developers should note that because of IL s stronger typing system there is no performance penalty associated with the use of exceptions with IL in the way that there is in C Also the finally block which has long been on many C developers wish list is supported by NET and by C Exceptions are covered in detail in Chapter 13 Errors and Exceptions Briefly the idea is that certain areas of code are designated as exception handler routines with each one able to deal with a particular 16 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 17 F Chapter 1 NET Architecture error condition for example a file not being found or being denied permission to perform some opera tion These conditions can be define
40. rivate assemblies Because a private assembly is entirely self contained the process of deploying it is simple You simply place the appropriate file s in the appropriate folder in the file system no registry entries need to be made This process is known as zero impact xcopy installation Shared Assemblies Shared assemblies are intended to be common libraries that any other application can use Because any other software can access a shared assembly more precautions need to be taken against the following risks Q Name collisions where another company s shared assembly implements types that have the same names as those in your shared assembly Because client code can theoretically have access to both assemblies simultaneously this could be a serious problem Q The risk of an assembly being overwritten by a different version of the same assembly the new version being incompatible with some existing client code The solution to these problems involves placing shared assemblies in a special directory subtree in the file system known as the global assembly cache GAC Unlike with private assemblies this cannot be done by simply copying the assembly into the appropriate folder it needs to be specifically installed into the cache This process can be performed by a number of NET utilities and involves carrying out certain checks on the assembly as well as setting up a small folder hierarchy within the assembly cache that is used
41. s for Web pages without having to worry about how to ensure that your page will run on any of the available browsers because Web Forms will take care of that for you You can use C or Visual Basic 2005 to expand the Web Form toolbox Creating a new server side control is simply a matter of implementing NET s System Web UI WebControls WebControl class XML Web Services Today HTML pages account for most of the traffic on the World Wide Web With XML however computers have a device independent format to use for communicating with each other on the Web In the future computers may use the Web and XML to communicate information rather than dedicated lines and pro prietary formats such as Electronic Data Interchange EDI XML Web services are designed for a service oriented Web in which remote computers provide each other with dynamic information that can be analyzed and reformatted before final presentation to a user An XML Web service is an easy way for a computer to expose information to other computers on the Web in the form of XML In technical terms an XML Web service on NET is an ASP NET page that returns XML instead of HTML to requesting clients Such pages have a code behind DLL containing a class that derives from the WebService class The Visual Studio 2005 IDE provides an engine that facilitates Web service development An organization might choose to use XML Web services for two main reasons The first reason is that the
42. s they are on Windows NT 2000 XP 2003 so the theoretical possibility exists of applications crashing Windows by writing to inappropriate memory Processes don t just serve as a way to isolate instances of running code from each other On Windows NT 2000 XP 2003 systems they also form the unit to which security privileges and permissions are assigned Each process has its own security token which indicates to Windows precisely what operations that process is permitted to do Although processes are great for security reasons their big disadvantage is in the area of performance Often a number of processes will actually be working together and therefore need to communicate with each other The obvious example of this is where a process calls up a COM component which is an exe cutable and therefore is required to run in its own process The same thing happens in COM when surro gates are used Because processes cannot share any memory a complex marshaling process has to be used to copy data between the processes This results in a very significant performance hit If you need compo nents to work together and don t want that performance hit then you have to use DLL based components and have everything running in the same address space with the associated risk that a badly behaved component will bring everything else down Application domains are designed as a way of separating components without resulting in the perform ance problems ass
43. sm for handling errors which involves returning error codes from methods and passing error objects around The fact that exceptions are handled consistently in different languages is a crucial aspect of facilitating multilanguage development Use of Attributes Attributes are a feature that is familiar to developers who use C to write COM components through their use in Microsoft s COM Interface Definition Language IDL The initial idea of an attribute was that it provided extra information concerning some item in the program that could be used by the compiler Attributes are supported in NET and hence now by C C and Visual Basic 2005 What is how ever particularly innovative about attributes in NET is that a mechanism exists whereby you can define your own custom attributes in your source code These user defined attributes will be placed with the metadata for the corresponding data types or methods This can be useful for documentation purposes where they can be used in conjunction with reflection technology in order to perform pro gramming tasks based on attributes Also in common with the NET philosophy of language inde pendence attributes can be defined in source code in one language and read by code that is written in another language Attributes are covered in Chapter 12 Reflection Assemblies An assembly is the logical unit that contains compiled code targeted at the NET Framework Assemblies are not cover
44. syntax for code has significant advantages Platform Independence First it means that the same file containing byte code instructions can be placed on any platform at run time the final stage of compilation can then be easily accomplished so that the code will run on that par ticular platform In other words by compiling to IL you obtain platform independence for NET in much the same way as compiling to Java byte code gives Java platform independence 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 5 F Chapter 1 NET Architecture You should note that the platform independence of NET is only theoretical at present because at the time of writing a complete implementation of NET is only available for Windows However a partial imple mentation is available see for example the Mono project an effort to create an open source implementation of NET at www go mono com Performance Improvement Although we previously made comparisons with Java IL is actually a bit more ambitious than Java byte code IL is always Just in Time compiled known as JIT compilation whereas Java byte code was often interpreted One of the disadvantages of Java was that on execution the process of translating from Java byte code to native executable resulted in a loss of performance with the exception of more recent cases where Java is JIT compiled on certain platforms Instead of compiling the entire application in one go which could lead to a slow s
45. t CLS compliant code should not expose any two names that differ only in their case Therefore Visual Basic 2005 code can work with CLS compliant code This example shows that the CLS works in two ways First it means that individual compilers do not have to be powerful enough to support the full features of NET this should encourage the development of compilers for other programming languages that target NET Second it provides a guarantee that if 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 13 F Chapter 1 NET Architecture you restrict your classes to exposing only CLS compliant features code written in any other compliant language can use your classes The beauty of this idea is that the restriction to using CLS compliant features applies only to public and protected members of classes and public classes Within the private implementations of your classes you can write whatever non CLS code you want because code in other assemblies units of managed code see later in this chapter cannot access this part of your code anyway We won t go into the details of the CLS specifications here In general the CLS won t affect your C code very much because there are very few non CLS compliant features of C anyway Garbage Collection The garbage collector is NET s answer to memory management and in particular to the question of what to do about reclaiming memory that running applications ask for Up until now two techniques have bee
46. t was often a vexing challenge to configure InterDev and the project s Web server to turn debugging on For maximum clarity the ASP NET code behina feature lets you take the structured approach even fur ther ASP NET allows you to isolate the server side functionality of a page to a class compile that class into a DLL and place that DLL into a directory below the HTML portion A code behind directive at the top of the page associates the file with its DLL When a browser requests the page the Web server fires the events in the class in the page s code behind DLL Last but not least ASP NET is remarkable for its increased performance Whereas classic ASP pages are interpreted with each page request the Web server caches ASP NET pages after compilation This means that subsequent requests of an ASP NET page execute more quickly than the first ASP NET also makes it easy to write pages that cause forms to be displayed by the browser which you might use in an intranet environment The traditional wisdom is that form based applications offer a 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 23 F Chapter 1 NET Architecture richer user interface but are harder to maintain because they run on so many different machines For this reason people have relied on form based applications when rich user interfaces were a necessity and extensive support could be provided to the users Web Forms To make Web page construction even easier Visual
47. tartup time the JIT com piler simply compiles each portion of code as it is called just in time When code has been compiled once the resultant native executable is stored until the application exits so that it does not need to be recompiled the next time that portion of code is run Microsoft argues that this process is more efficient than compiling the entire application code at the start because of the likelihood that large portions of any application code will not actually be executed in any given run Using the JIT compiler such code will never be compiled This explains why we can expect that execution of managed IL code will be almost as fast as executing native machine code What it doesn t explain is why Microsoft expects that we will get a performance improvement The reason given for this is that because the final stage of compilation takes place at runtime the JIT compiler will know exactly what processor type the program will run on This means that it can optimize the final executable code to take advantage of any features or particular machine code instruc tions offered by that particular processor Traditional compilers will optimize the code but they can only perform optimizations that are independ ent of the particular processor that the code will run on This is because traditional compilers compile to native executable before the software is shipped This means that the compiler doesn t know what type of processor the c
48. ther language Q The class can contain an instance of another class no matter what the languages of the two classes are A An object can directly call methods against another object written in another language O Objects or references to objects can be passed around between methods Q When calling methods between languages you can step between the method calls in the debugger even when this means stepping between source code written in different languages This is all quite an ambitious aim but amazingly NET and IL have achieved it In the case of stepping between methods in the debugger this facility is really offered by the Visual Studio NET integrated development environment IDE rather than by the CLR itself Distinct Value and Reference Types As with any programming language IL provides a number of predefined primitive data types One char acteristic of IL however is that it makes a strong distinction between value and reference types Value types are those for which a variable directly stores its data whereas reference types are those for which a variable simply stores the address at which the corresponding data can be found In C terms using reference types can be considered to be similar to accessing a variable through a pointer whereas for Visual Basic the best analogy for reference types are objects which in Visual Basic 6 are always accessed through references IL also lays down specifications about data stor
49. thin a Microsoft environment is something that was introduced in 2006 and is part of the NET Framework 3 0 This means that in order to run any WPF application you are going to need to make sure that the NET Framework 3 0 is installed on the client machine WPF applications will be available for Windows Vista Windows XP and Windows Server 2003 the only operating systems which allow for the installation of the INET Framework 3 0 XAML is the XML declaration that is used to create a form which represents all the visual aspect and behaviors of the WPF application While it is possible to work with a WPF application programmatically WPF is a step in the direction of declarative programming which the industry is moving to Declarative programming means that instead of creating objects through programming in a compiled language such as C VB or Java instead you declare everything through XML type programming Chapter 31 Windows Presentation Foundation goes into detail on how to build these new types of applications using XAML and C Windows Controls Although Web Forms and Windows Forms are developed in much the same way you use different kinds of controls to populate them Web Forms use Web server controls and Windows Forms use Windows Controls A Windows Control is a lot like an ActiveX control After a Windows Control is implemented it com piles to a DLL that must be installed on the client s machine In fact the NET SDK provid
50. to ensure assembly integrity To avoid the risk of name collisions shared assemblies are given a name based on private key cryptog raphy private assemblies are simply given the same name as their main file name This name is known as a strong name is guaranteed to be unique and must be quoted by applications that reference a shared assembly Problems associated with the risk of overwriting an assembly are addressed by specifying version infor mation in the assembly manifest and by allowing side by side installations Reflection Because assemblies store metadata including details of all the types and members of these types that are defined in the assembly it is possible to access this metadata programmatically Full details of this are given in Chapter 12 Reflection This technique known as reflection raises interesting possibilities because it means that managed code can actually examine other managed code or can even examine itself to determine information about that code This is most commonly used to obtain the details of attributes although you can also use reflection among other purposes as an indirect way of instantiat ing classes or calling methods given the names of those classes on methods as strings In this way you could select classes to instantiate methods to call at runtime rather than compile time based on user input dynamic binding 19 24727c01 Pa qxd WroxPro 5 7 07 12 12 PM Page 20 F rt l
51. ts can easily be manipulated using the ADO NET object model and automatically render as XML for transport across an office intranet Once a database schema has been established for a new project C presents an excellent medium for implementing a layer of data access objects each of which could provide insertion updates and deletion access to a different database table Because it s the first component based C language C is a great language for implementing a business object tier too It encapsulates the messy plumbing for intercomponent communication leaving devel opers free to focus on gluing their data access objects together in methods that accurately enforce their organizations business rules Moreover with attributes C business objects can be outfitted for method level security checks object pooling and JIT activation supplied by COM Services Furthermore NET ships with utility programs that allow your new NET business objects to interface with legacy COM components 25 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 26 F Part The CF Language To create an enterprise application with C you create a Class Library project for the data access objects and another for the business objects While developing you can use Console projects to test the methods on your classes Fans of extreme programming can build Console projects that can be executed automati cally from batch files to unit test that working code has not been bro
52. w you take a more detailed look at the Microsoft Intermediate Language MSIL or simply IL the assembly language that all compiled code ends up in on NET In particular you see how IL in partnership with the Common Type System CTS and Common Language Specification CLS works to give you interoperability between lan guages that target NET This chapter also discusses where common languages including Visual Basic and C fit into NET Next you move on to examine some of the other features of NET including assemblies name spaces and the NET base classes The chapter finishes with a brief look at the kinds of applica tions you can create as a C developer 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 4 F Part The CF Language The Relationship of C to NET C is a relatively new programming language and is significant in two respects Q Itis specifically designed and targeted for use with Microsoft s NET Framework a feature rich platform for the development deployment and execution of distributed applications Q It is a language based on the modern object oriented design methodology and when designing it Microsoft learned from the experience of all the other similar languages that have been around since object oriented principles came to prominence some 20 years ago One important thing to make clear is that C is a language in its own right Although it is designed to generate code that targets the NET environme
53. y rely on HTTP XML Web services can use existing networks HTTP as a medium for conveying information The other is that because XML Web services use XML the data format is self describing nonproprietary and platform independent 23 24727c01 qxd WroxPro 5 7 07 12 12 PM Page 24 F Part The CF Language Creating Windows Forms Although C and NET are particularly suited to Web development they still offer splendid support for so called fat client or thick client apps applications that have to be installed on the end user s machine where most of the processing takes place This support is from Windows Forms A Windows Form is the NET answer to a Visual Basic 6 Form To design a graphical window interface you just drag controls from a toolbox onto a Windows Form To determine the window s behavior you write event handling routines for the form s controls A Windows Form project compiles to an executable that must be installed alongside the NET runtime on the end user s computer Like other NET project types Windows Form projects are supported by both Visual Basic 2005 and C Chapter 28 Windows Forms examines Windows Forms more closely Using the Windows Presentation Foundation WPF One of the newest technologies to hit the block is the Windows Presentation Foundation WPF WPF makes use of XAML in building applications XAML stands for Extensible Application Markup Language This new way of creating applications wi
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