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1. dependent static simple a_type variable3 not dependent template lt class T gt typename T a_ type dependent example lt T gt variablel 0 not a type template lt class T gt typename parametric lt T gt a_type dependent example lt T gt variable2 0 not a type template lt class T gt simple a_type not dependent example lt T gt variable3 0 not a type Nesting Template Declarations Because the gt gt character sequence is interpreted as the right shift operator you must be careful when you use one template declaration inside another Make sure you separate adjacent gt characters with at least one blank space For example the following ill formed statement Array lt String lt 10 gt gt short_string_array 100 gt gt right shift is interpreted as Array lt String lt 10 gt gt short_string_array 100 Templates 31 The correct syntax is Array lt String lt 10 gt gt short_string_array 100 32 C Programming Guide Revision A February 1999 CHAPTER 5 Exception Handling This chapter explains exception handling as currently implemented in the Sun C compiler and the requirements of the C International Standard For additional information on exception handling see The C Programming Language third edition by Bjarne Stroustrup Addison Wesley 1997 Understanding Exception Handling Exceptions are anomalies that occur during the normal flow of a
2. February 1999 Index Index 63
3. between pointer to member types and between pointer to function types Usage of the reinterpret_cast operator can have undefined or implementation dependent results The following points describe the only ensured behavior m A pointer to a data object or to a function but not a pointer to member can be converted to any integer type large enough to contain it Type long is always big enough to contain a pointer value on the architectures supported by Sun C When converted back to its original type the value will be the same as it originally was m A pointer to a nonmember function can be converted to a pointer to a different nonmember function type If converted back to the original type the value will be the same as it originally was m A pointer to an object can be converted to a pointer to a different object type provided that the new type has alignment requirements no stricter than the original type If converted back to the original type the value will be the same as it originally was a An lvalue of type T1 can be converted to a type reference to T2 if an expression of type pointer to T1 can be converted to type pointer to T2 with a reinterpret cast m An rvalue of type pointer to member of X of type T1 can be explicitly converted to an rvalue of type pointer to member of Y of type T2 if T1 and T2 are both function types or both object types C Programming Guide Revision A February 1
4. described in this book and the companion book C User s Guide is available under the Solaris 2 5 1 2 6 and Solaris 7 operating environments on the hardware platforms in SPARC and x86 Sun C 5 0 implements the language and libraries described in the C International Standard The C Language C was first described in The C Programming Language by Bjarne Stroustrup and later more formally described in The Annotated C Reference Manual by Margaret Ellis and Bjarne Stroustrup An international standard for C is now available C is designed as a superset of the C programming language While retaining efficient low level programming C adds m Stronger type checking m Extensive data abstraction features m Support for object oriented programming m Synchronous exception handling a A large standard library The support for object oriented programming allows good design of modular and extensible interfaces among program modules The standard library including an extensible set of data types and algorithms speeds the development of common applications Data Abstraction C directly supports the use of programmer defined data types that function much like the predefined data types already in the language Such abstract data types can be defined to model the problem being solved Object Oriented Features The class the fundamental unit of data abstraction in C contains data and defines operations on the data A
5. in one thread affects only the exceptions in that thread The default function for terminate is abort for the main thread and thr_exit for other threads see Specifying Runtime Errors on page 38 Note Thread cancellation pthread_cancel 3T results in the destruction of automatic local nonstatic objects on the stack When a thread is cancelled the execution of local destructors is interleaved with the execution of cleanup routines that the user has registered with pthread_cleanup_push The local objects for functions called after a particular cleanup routine is registered are destroyed before that routine is executed Exception Handling 45 46 C Programming Guide Revision A February 1999 CHAPTER 6 Runtime Type Identification This chapter explains the use of Runtime Type Identification RTTI Use this feature while a program is running to find out type information that you could not determine at compile time Static and Dynamic Types In C pointers to classes have a static type the type written in the pointer declaration and a dynamic type which is determined by the actual type referenced The dynamic type of the object could be any class type derived from the static type In the following example ap has the static type A and a dynamic type B class A class B public A extern B bv extern A ap amp bv RTTI allows the programmer to determine the dynamic type of the pointer
6. objects of the type BigNum then the expression has a value determined by your definition of for BigNum nl n2 In the absence of an operator that you define the operation would not be allowed on a class type The operator is predefined only for the built in numeric types such as int long or float Operators with such extra definitions are called overloaded operators The data storage elements in a C class are called data members The operations in a C class include both functions and overloaded built in operators special kinds of functions A class s functions can be member functions declared as part of the class or nonmember functions declared outside the class Member functions exist to operate on members of the class Nonmember functions must be declared friend functions if they need to access private or protected members of the class directly You can specify the level of access for a class member using the public private and protected member access specifiers Public members are available to all functions in the program Private members are available only to member functions and friend functions of the class Protected members are available only to members and friends of the base class and members and friends of derived classes You can apply the same access specifiers to base classes limiting access to all members of the affected base class Compatibility With C C was designed to be highly compatibl
7. If the original function s exception specification does not allow std bad_exception function 40 C Programming Guide Revision A February 1999 terminate is called immediately Otherwise exception handling continues as though the original function had really thrown std bad_exception unexpected calls the function passed as an argument to set_unexpected Such a function takes no parameters returns no value and must not return to its caller The function passed in the most recent call to set_unexpected is called The previous function passed as an argument to set_unexpected is the return value so you can implement a stack strategy for using unexpected Note Selecting an unexpected replacement that returns to its caller is an error Calling the uncaught_exception Function An uncaught or active exception is an exception that has been thrown but not yet accepted by a handler The function uncaught_exception returns true if there is an uncaught exception and false otherwise The uncaught_exception function is most useful for preventing program termination due to a function that exits with an uncaught exception while another exception is still active This situation most commonly occurs when a destructor called during stack unwinding throws an exception To prevent this situation make sure uncaught_exception returns false before throwing an exception within a destructor Another way to prevent program t
8. a template parameter so they refer to a global variable However cin and cout must have the same definition everywhere C Programming Guide Revision A February 1999 Local Types as Template Arguments The template instantiation system relies on type name equivalence to determine which templates need to be instantiated or reinstantiated Thus local types can cause serious problems when used as template arguments Beware of creating similar problems in your code For example array h template lt class Type gt class Array Type data int size public Array int sz int GetSize array cc template lt class Type gt Array lt Type gt Array int sz size sz data new Typelsize l template lt class Type gt int Array lt Type gt GetSize return size filel cc include array h struct Foo int data Array lt Foo gt FilelData file2 cc include array h struct Foo double data Array lt Foo gt File2Data The Foo type as registered in filel cc is not the same as the Foo type registered in file2 cc Using local types in this way could lead to errors and unexpected results Friend Declarations of Template Functions Templates must be declared before they are used A friend declaration constitutes a use of the template not a declaration of the template A true template declaration must precede the friend declaration For example when the compilation system attempts to link the produced obj
9. amp SUN microsystems C Programming Guide 901 San Antonio Road Palo Alto CA 94303 4900 USA 650 960 1300 fax 650 969 9131 Part No 805 4955 Revision A February 1999 Copyright Copyright 1999 Sun Microsystems Inc 901 San Antonio Road Palo Alto California 94303 4900 U S A All rights reserved All rights reserved This product or document is protected by copyright and distributed under licenses restricting its use copying distribution and decompilation No part of this product or document may be reproduced in any form by any means without prior written authorization of Sun and its licensors if any Portions of this product may be derived from the UNIX system licensed from Novell Inc and from the Berkeley 4 3 BSD system licensed from the University of California UNIX is a registered trademark in the United States and in other countries and is exclusively licensed by X Open Company Ltd Third party software including font technology in this product is protected by copyright and licensed from Sun s suppliers RESTRICTED RIGHTS Use duplication or disclosure by the U S Government is subject to restrictions of FAR 52 227 14 g 2 6 87 and FAR 52 227 19 6 87 or DFAR 252 227 7015 b 6 95 and DFAR 227 7202 3 a Sun Sun Microsystems the Sun logo SunDocs SunExpress Solaris Sun Performance Library Sun Performance WorkShop Sun Performance WorkShop Fortran Sun Visual WorkShop Sun WorkShop Sun WorkShop Compiler
10. and UNIX commands How This Book Is Organized This book contains the following chapters Chapter 1 Introduction briefly describes the features of the compiler Chapter 2 Program Organization discusses header files inline function definitions and template definitions Chapter 3 Pragmas provides information on using pragmas or directives to pass specific information to the compiler Chapter 4 Templates discusses the definition and use of templates Chapter 5 Exception Handling discusses the Sun C 5 0 compiler s implementation of exception handling Chapter 6 Runtime Type Identification explains RTTI and introduces the RTTI options supported by the compiler Preface vii Chapter 7 Cast Operations describes new cast operations Chapter 9 Performance explains how to improve the performance of C functions Multiplatform Release Note The name of the latest Solaris operating environment release is Solaris 7 but code and path or package path names may use Solaris 2 7 or SunOS 5 7 The Sun WorkShop documentation applies to Solaris 2 5 1 Solaris 2 6 and Solaris 7 operating environments on m The SPARC platform m The x86 platform where x86 refers to the Intel implementation of one of the following Intel 80386 Intel 80486 Pentium or the equivalent Note The term x86 refers to the Intel 8086 family of microprocessor chips including the Pentium Pentium Pro and Pentium II
11. ap abp is non null so ap was a pointer to an AB object go ahead and use abp process_AB abp else abp is null so ap was NOT a pointer to an AB object do not use abp process_not_AB ap In compatibility mode compat 4 if runtime type information has not been enabled with the features rtti compiler option the compiler converts dynamic_cast to static_cast and issues a warning See Chapter 5 If exceptions have been disabled the compiler converts dynamic_cast lt T amp gt to static_cast lt T gt and issues a warning The dynamic cast to a reference might require an exception in normal circumstances See Chapter 4 Dynamic cast is necessarily slower than an appropriate design pattern such as conversion by virtual functions See Design Patterns Elements of Reusable Object Oriented Software by Erich Gamma Addison Wesley 1994 56 C Programming Guide Revision A February 1999 CHAPTER 8 Performance You can improve the performance of C functions by writing those functions in a manner that helps the compiler do a better job of optimizing them Many books have been written on software performance in general and C in particular For example see Tom Cargill C Programming Style Addison Wesley 1992 Jon Louis Bentley Writing Efficient Programs Prentice Hall 1982 and Scott Meyers Effective C Addison Wesley 1992 This chapter does not repeat such valuable information but discu
12. cannot resolve a weak symbol The following directive defines bar to be a weak symbol No error messages are generated if the linker cannot find a definition for a function named bar pragma weak bar The following directive instructs the linker to resolves any references to bar to bar if it is defined anywhere in the program and to foo otherwise C Programming Guide Revision A February 1999 pragma weak bar foo You must declare a function before you use it in a weak pragma For example extern void bar int extern void _bar int pragma weak _bar bar The effects of using pragma weak are If your program calls but does not define function namel the linker uses the definition from the library m If your program defines its own version of function namel then the program definition is used and the weak global definition of function namel in the library is not used m If the program directly calls function name2 the definition from the library is used a duplicate definition of function name2 causes an error See the Solaris Linker and Libraries Guide for more information Note The names in the pragma must be the names a seen by the linker which means the mangled name if the function has C linkage Pragmas 17 18 C Programming Guide Revision A February 1999 CHAPTER 4 Templates Templates make it possible for you to write a single body of code that applies to a wide range of types in a
13. class can build on one or more classes this property is called inheritance or derivation The inherited class or parent class is called a base class in C It is known as a super class in other programming languages The child class is called a derived class in C It is called a subclass in other programming languages A derived class has all the data and usually all the operations of its base classes It might add new data or replace operations from the base classes A class hierarchy can be designed to replace a base class with a derived class For example a Window class could have as a derived class a ScrollingWindow class that has all the properties of the Window class but also allows scrolling of its contents The ScrollingWindow class can then be used wherever the Window class is expected This substitution property is known as polymorphism meaning many forms A program is said to be object oriented when it is designed with abstract data types that use inheritance and exhibit polymorphism Type Checking A compiler or interpreter performs type checking when it ensures that operations are applied to data of the correct type C has stronger type checking than C though not as strong as that provided by Pascal which always prohibits attempts to use data of the wrong type The C compiler produces errors in some cases but in others it converts data to the correct type In addition to having the C compiler perform t
14. from Sun Microsystems Inc If you live in the United States Canada Europe or Japan you can purchase documentation sets or individual manuals using this program For a list of documents and how to order them see the catalog section of the SunExpress Internet site at http www sun com sunexpress C Programming Guide Revision A February 1999 Accessing Sun Documents Online Sun WorkShop documentation is available online from several sources m The docs sun com Web site m AnswerBook2 collections HTML documents m Online help and release notes Using the docs sun com Web site The docs sun com Web site enables you to access Sun technical documentation online You can browse the docs sun com archive or search for a specific book title or subject The URL is http docs sun com Accessing AnswerBook2 Collections The Sun WorkShop documentation is also available using AnswerBook2 software To access the AnswerBook2 collections your system administrator must have installed the AnswerBook2 documents during the installation process if the documents are not installed see your system administrator or Chapter 3 of Sun WorkShop Quick Install for installation instructions For information about accessing AnswerBook2 documents see Chapter 6 of Sun WorkShop Quick Install Solaris installation documentation or your system administrator Note To access AnswerBook2 documents Solaris 2 5 1 users must first download AnswerBook2 do
15. function passed in the most recent call to set_terminate is called The previous function passed as an argument to set_terminate is the return value so you can implement a stack strategy for using terminate The default function for terminate calls abort for the main thread and thr_exit for other threads Note that thr_exit does not unwind the stack or call C destructors for automatic objects Note Selecting a terminate replacement that returns to its caller or that does not terminate the program or thread is an error set_unexpected You can modify the default behavior of unexpected by calling the function set_unexpected declarations are in standard header lt exception gt namespace std class exception class bad_exception typedef void unexpected_handler unexpected_handler set_unexpected unexpected_handler f throw void unexpected The unexpected function is called when a function attempts to exit via an exception not listed in its exception specification The default version of unexpected calls terminate A replacement version of unexpected might throw an exception permitted by the violated exception specification If it does so exception handling continues as though the original function had really thrown the replacement exception If the replacement for unexpected throws any other exception that exception is replaced by the standard exception std bad_exception
16. handlers for the base class to ensure that the handler for the derived class can be invoked Checking Access Control in Exceptions The compiler performs the following check on access control on exceptions m The formal argument of a catch clause obeys the same rules as an argument of the function in which the catch clause occurs m An object can be thrown if it can be copied and destroyed in the context of the function in which the throw occurs Currently access controls do not affect matching No other access is checked at runtime except for the matching rule described in Matching Exceptions With Handlers on page 41 Enclosing Functions in t ry Blocks If the constructor for a base class or member of a class T exits via an exception there would ordinarily be no way for the T constructor to detect or handle the exception The exception would be thrown before the body of the T constructor is entered and thus before any try block in T could be entered A new feature in C is the ability to enclose an entire function in a try block For ordinary functions the effect is no different from placing the body of the function in a try block But for a constructor the try block traps any exceptions that escape from initializers of base classes and members of the constructor s class When the entire function is enclosed in a try block the block is called a function try block 42 C Programming Guide Revision A February 1999 I
17. i 0 i lt num elems 1 i for int F itl j lt num_elems j if store j 1 gt store j Elem temp store j store j store j 1 store j 1 temp The preceding example defines a sort function over the predeclared Array class template objects The next example shows the actual use of the sort function Array lt int gt int_array 100 construct an array of ints sort int_array sort it Default Template Parameters You can give default values to template parameters for class templates but not function templates template lt class Elem int gt class Array template lt unsigned Size 100 gt class String If a template parameter has a default value all parameters after it must also have default values A template parameter can have only one default value Template Specialization There may be performance advantages to treating some combinations of template arguments as a special case as in the following examples for twice Alternatively a template description might fail to work for a set of its possible arguments as in the following examples for sort Template specialization allows you to define alternative implementations for a given combination of actual template arguments The template specialization overrides the default instantiation C Programming Guide Revision A February 1999 Template Specialization Declaration You must declare a specialization before any use of that c
18. m Variable declarations are allowed anywhere a statement may appear They may also occur within the header of an if switch or loop statement not just at the beginning of the block m Anew comment marker begins a comment that extends to the end of the line m The name of an enumeration or class is automatically a type name m Default values can be assigned to function parameters m Inline functions can replace a function call with the function body improving program efficiency without resorting to macros C Programming Guide Revision A February 1999 CHAPTER 2 Program Organization The file organization of a C program requires more care than is typical for a C program This chapter describes how to set up your header files inline function definitions and template definitions Header Files Creating an effective header file can be difficult Often your header file must adapt to different versions of both C and C To accommodate templates make sure your header file is tolerant of multiple inclusions idempotent and is self contained Language Adaptable Header Files You might need to develop header files for inclusion in both C and C programs However Kernighan and Ritchie C K amp R C also known as classic C ANSI C Annotated Reference Manual C ARM C and ISO C sometimes require different declarations or definitions for the same program element within a single header file See the C Migration Guid
19. profile of a program Links incrementally allowing insertion of modified object code into a previously built executable Expands assembler inline procedure calls C Programming Guide Revision A February 1999 TABLE P 2 Man Pages Related to C continued Title lex rpcgen version yacc Description Generates lexical analysis programs Generates C C code to implement an RPC protocol Displays version identification of object file or binary Converts a context free grammar into a set of tables for a simple automaton that executes an LALR 1 parsing algorithm README file The README file highlights important information about the compiler including m New and changed features m Software incompatibilities m Current software bugs a Information discovered after the manuals were printed README files are in opt install dir SUNWspro READMES To view the C compiler README file type SCC readme What Typographic Changes Mean The following table describes the typographic changes used in this book XV TABLE P 3 Typographic Conventions Typeface or Symbol AaBbCc123 AaBbCc123 AaBbCc123 AaBbCc123 Meaning The names of commands files and directories on screen computer output What you type contrasted with on screen computer output Command line placeholder replace with a real name or value Book titles new words or terms or word
20. program and prevent it from continuing These anomalies user logic or system errors can be detected by a function If the detecting function cannot deal with the anomaly it throws an exception A function that handles that kind of exception catches it In C when an exception is thrown it cannot be ignored there must be some kind of notification or termination of the program If no user provided exception handler is present the compiler provides a default mechanism to terminate the program Exception handling is expensive compared to ordinary program flow controls such as loops or if statements It is therefore better not to use the exception mechanism to deal with ordinary situations but to reserve it for situations that are truly unusual Exceptions are particularly helpful in dealing with situations that cannot be handled locally Instead of propagating error status throughout the program you can transfer control directly to the point where the error can be handled For example a function might have the job of opening a file and initializing some associated data If the file cannot be opened or is corrupted the function cannot do its job However that function might not have enough information to handle the problem The function can throw an exception object that describes the problem transferring control to an earlier point in the program The exception handler might 33 automatically try a backup file query
21. the directive has the effect of natural alignment Pragmas 15 16 TABLE 3 1 Strictest Alignment by Platform Strictest Platform Alignment x86 4 SPARC generic v7 v8 v8a v8plus v8plusa 8 SPARC v9 v9a 16 A pack directive applies to all structure definitions which follow it until the next pack directive If the same structure is defined in different translation units with different packing your program may fail in unpredictable ways In particular you should not use a pack directive prior to including a header defining the interface of a precompiled library The recommended usage is to place the pack directive in your program code immediately before the structure to be packed and to place pragma pack immediately after the structure pragma unknown_control_flow name name Use unknown_control_flow to specify a list of routines that violate the usual control flow properties of procedure calls For example the statement following a call to set jmp can be reached from an arbitrary call to any other routine The statement is reached by a call to long jmp Because such routines render standard flowgraph analysis invalid routines that call them cannot be safely optimized hence they are compiled with the optimizer disabled pragma weak function namel function name2 Use weak to define a weak global symbol This pragma is used mainly in source files for building libraries The linker does not warn you if it
22. the identifiers before using them in the pragma pragma fini identifier identifier Use fini to mark identifier as a finalization function Such functions are expected to be of type void to accept no arguments and to be called either when a program terminates under program control or when the containing shared object is removed from memory As with initialization functions finalization functions are executed in the order processed by the link editor In a source file the functions specified in pragma fini are executed after the static destructors in that file You must declare the identifiers before using them in the pragma pragma ident string Use ident to place string in the comment section of the executable pragma pack n Use pack to affect the packing of structure members If present n must be 0 or a power of 2 A value of other than 0 instructs the compiler to use the smaller of n byte alignment and the platform s natural alignment for the data type For example the following directive causes the members of all structures defined after the directive and before subsequent pack directives to be aligned no more strictly than on 2 byte boundaries even if the normal alignment would be on 4 or 8 byte boundaries pragma pack 2 When n is 0 or omitted the member alignment reverts to the natural alignment values If the value of n is the same as or greater than the strictest alignment on the platform
23. the type pointed referred to by v the conversion is equivalent to static_cast lt T gt v Casting to void If T is void the result is a pointer to the complete object That is v might point to one of the base classes of some complete object In that case the result of dynamic_cast lt void gt v is the same as if you converted v down the hierarchy to the type of the complete object whatever that is and then to void When casting to void the hierarchy must be polymorphic have virtual functions The result is checked at runtime Casting Down or Across the Hierarchy When casting down or across the hierarchy the hierarchy must be polymorphic have virtual functions The result is checked at runtime The conversion from v to T is not always possible when casting down or across a hierarchy For example the attempted conversion might be ambiguous T might be inaccessible or v might not point or refer to an object of the necessary type If the 54 C Programming Guide Revision A February 1999 runtime check fails and T is a pointer type the value of the cast expression is a null pointer of type T If T is a reference type nothing is returned there are no null references in C and the standard exception std bad_cast is thrown When you assume the following declarations class A ft public virtual void f Jz class B public virtual void g J class AB public virtual A private B The following f
24. type safe manner This chapter introduces template concepts and terminology in the context of function templates discusses the more complicated and more powerful class templates and the composition of templates Also discussed are template instantiation default template parameters and template specialization The chapter concludes with a discussion of potential problem areas for templates Function Templates A function template describes a set of related functions that differ only by the types of their arguments or return values C 5 0 does not support non type template parameters for function templates Function Template Declaration You must declare a template before you can use it A declaration as in the following example provides enough information to use the template but not enough information to implement the template template lt class Number gt Number twice Number original In this example Number is a template parameter it specifies the range of functions that the template describes More specifically Number is a template type parameter and its 19 20 use within template declarations and definitions stands for some to be determined type Function Template Definition If you declare a template you must also define it A definition provides enough information to implement the template The following example defines the template declared in the previous example template lt class Number gt Number
25. unions are passed differently on different architectures On SPARC V7 V8 structs and unions are passed and returned by allocating storage within the caller and passing a pointer to that storage That is all structs and unions are passed by reference On SPARC V9 structs with a size no greater than 16 bytes 32 bytes are passed returned in registers Unions and all other structs are passed and returned by allocating storage within the caller and passing a pointer to that storage That is small structs are passed in registers unions and large structs are passed by reference As a consequence small value classes are passed as efficiently as primitive types On x86 structs and unions are passed by allocating space on the stack and copying the argument onto the stack Structs and unions are returned by allocating a 60 C Programming Guide Revision A February 1999 temporary object in the caller s frame and passing the address of the temporary object as an implicit first parameter Cache Member Variables Accessing member variables is a common operation in C member functions The compiler must often load member variables from memory through the this pointer Because values are being loaded through a pointer the compiler sometimes cannot determine when a second load must be performed or whether the value loaded before is still valid In these cases the compiler must choose the safe but slow approach and reload the member vari
26. 999 a Inall allowed cases a null pointer of one type when converted to a null pointer of a different type remains a null pointer m The reinterpret_cast operator cannot be used to cast away const use const_cast for that purpose m The reinterpret_cast operator should not be used to convert between pointers to different classes that are in the same class hierarchy use a static or dynamic cast for that purpose reinterpret_cast does not perform the adjustments that might be needed This is illustrated in the following example class A int a class B public A int b c void use_of_reinterpret_cast A al long 1 reinterpret_cast lt long gt amp al A ap reinterpret_cast lt A gt l safe B bp reinterpret_cast lt B gt amp al unsafe const A a2 ap reinterpret_cast lt A gt amp a2 error const removed static cast The expression static_cast lt T gt v converts the value of the expression v to that of type T It can be used for any type conversion that is allowed implicitly In addition any value may be cast to void and any implicit conversion can be reversed if that cast would be legal as an old style cast class B EES class C public B enum E first 1 second 2 third 3 void use_of_static_cast C cl B bp cl implicit conversion C c2 static_cast lt C gt bp reverse implicit conversion int i second implicit conversion E e static_c
27. Definitions You can organize your inline function definitions in two ways with definitions inline and with definitions included Each approach has advantages and disadvantages Definitions Inline You can use the definitions inline organization only with member functions Place the body of the function directly following the function declaration within the class definition class Class int method return 3 C Programming Guide Revision A February 1999 This organization avoids repeating the prototype of the function reduces the bulk of source files and the chance for inconsistencies However this organization can introduce implementation details into what would otherwise be read as an interface You would have to do significant editing if the function became non inline Use this organization only when the body of the function is trivial that is empty braces or the function will always be inline Definitions Included You can use the definitions included organization for all inline functions Place the body of the function together with a repeat if necessary of the prototype The function definition may appear directly within the source file or be included with the source file class Class int method inline int Class method return 3 This organization separates interface and implementation You can move definitions easily from header files to source files when the function is no longer im
28. Function Definitions 8 Definitions Inline 8 Definitions Included 9 Template Definitions 9 Definitions Included 9 Contents iii Definitions Separate 10 Pragmas 13 Pragma Forms 13 Pragma Reference 14 pragma align 14 pragma init 14 pragma fini 15 pragma ident 15 pragma pack n 15 pragma weak 16 Templates 19 Function Templates 19 Function Template Declaration 19 Function Template Definition 20 Function Template Use 20 Class Templates 21 Class Template Definition 21 Class Template Member Definitions Class Template Use 23 Template Instantiation 23 Implicit Template Instantiation 24 Whole Class Instantiation 24 Explicit Template Instantiation 24 Template Composition 25 Default Template Parameters 26 Template Specialization 26 pragma unknown_control_flow 16 22 Template Specialization Declaration 27 C Programming Guide Revision A February 1999 Template Specialization Definition 27 Template Specialization Use and Instantiation 27 Template Problem Areas 28 Nonlocal Name Resolution and Instantiation 28 Local Types as Template Arguments 29 Friend Declarations of Template Functions 29 Using Qualified Names Within Template Definitions 31 Exception Handling 33 Understanding Exception Handling 33 Using Exception Handling Keywords 34 try 34 catch 34 throw 35 Implementing Exception Handlers 35 Synchronous Exception Handling 36 Asynchronous Exception Handling 36 Managing Flow of Control 36 Branc
29. RTTI Options For C 5 0 in compatibility mode compat 4 RTTI support requires significant resources to implement RTTI is disabled by default in that mode To enable RTTI implementation and recognition of the associated typeid keyword use the option 47 48 features rtti To disable RTTI implementation and recognition of the associated typeid keyword use the option features no rtti the default For C 5 0 in standard mode the default mode RTTI does not have a significant impact on program compilation or execution In standard mode RTTI is always enabled typeid Operator The typeid operator produces a reference to an object of class type_info which describes the most derived type of the object To make use of the typeid function the source code must include the lt typeinfo gt header file The primary value of this operator class combination is in comparisons In such comparisons the top level const and volatile qualifiers are ignored as in the following example Note that in this example A and B are types which have default constructors include lt typeinfo gt include lt assert h gt void use_of_typeinfo A al const A a2 assert typeid al typeid a2 assert typeid A typeid const A assert typeid A typeid a2 assert typeid A typeid const A amp B bl assert typeid al typeid bl assert typeid A typeid B The typeid operator raises a bad_t ype
30. able each time it is accessed You can avoid unnecessary memory reloads by explicitly caching the values of member variables in local variables as follows m Declare a local variable and initialize it with the value of the member variable m Use the local variable in place of the member variable throughout the function m If the local variable changes assign the final value of the local variable to the member variable However this optimization may yield undesired results if the member function calls another member function on that object This optimization is most productive when the values can reside in registers as is the case with primitive types The optimization may also be productive for memory based values because the reduced aliasing gives the compiler more opportunity to optimize This optimization may be counter productive if the member variable is often passed by reference either explicitly or implicitly On occasion the desired semantics of a class requires explicit caching of member variables for instance when there is a potential alias between the current object and one of the member function s arguments For example complex amp operator complex left complex right left real left real right real left imag right imag left imag left real right imag left image right real will yield unintended results when called with X X Performance 61 62 C Programming Guide Revision A
31. ast lt E gt i reverse implicit conversion The static_cast operator cannot be used to cast away const You can use static_cast to cast down a hierarchy from a base to a derived pointer or reference but the conversion is not checked the result might not be usable Cast Operations 53 Dynamic Casts A pointer or reference to a class can actually point refer to any class derived from that class Occasionally it may be desirable to obtain a pointer to the fully derived class or to some other subobject of the complete object The dynamic cast provides this facility The dynamic type cast converts a pointer or reference to one class T1 into a pointer reference to another class T2 T1 and T2 must be part of the same hierarchy the classes must be accessible via public derivation and the conversion must not be ambiguous In addition unless the conversion is from a derived class to one of its base classes the smallest part of the hierarchy enclosing both T1 and T2 must be polymorphic have at least one virtual function In the expression dynamic_cast lt T gt v v is the expression to be cast and T is the type to which it should be cast T must be a pointer or reference to a complete class type one for which a definition is visible or a pointer to cv void where cv is an empty string const volatile or const volatile Casting Up the Hierarchy When casting up the hierarchy if T points or refers to a base class of
32. ate declaration For Function Members The definition of a template function member consists of the template parameter specification followed by a function definition The function identifier is qualified by the class template s class name and the template arguments The following example shows definitions of two function members of the Array class template which has a template parameter specification of template lt class Elem gt Each function identifier is qualified by the template class name and the template argument Array lt Elem gt template lt class Elem gt Array lt Elem gt Array int sz size sz data new Elem size template lt class Elem gt int Array lt Elem gt GetSize return size This example shows definitions of function members of the St ring class template include lt string h gt template lt unsigned Size gt int String lt Size gt length int len 0 while len lt Size amp amp data len 0 len return len template lt unsigned Size gt String lt Size gt String char initial strncpy data initial Size if length Size overflow C Programming Guide Revision A February 1999 For Static Data Members The definition of a template static data member consists of the template parameter specification followed by a variable definition where the variable identifier is qualified by the class template name and its template actual argume
33. ation A class template declaration provides only the name of the class and its template arguments Such a declaration is an incomplete class template The following example is a template declaration for a class named Array that takes any type as an argument template lt class Elem gt class Array This template is for a class named String that takes an unsigned integer as an argument template lt unsigned Size gt class String Class Template Definition A class template definition must declare the class data and function members as in the following examples template lt class Elem gt class Array Elem data int size public Array int sz int GetSize Elem amp operator int idx template lt unsigned Size gt class String char data Size static int overflows public String char initial int length Templates 21 22 Unlike function templates class templates can have both type parameters such as class Elem and expression parameters such as unsigned Size An expression parameter can be m A value that has an integral type or enumeration m A pointer or a reference to an object m A pointer or a reference to a function m A pointer to a class member function Class Template Member Definitions The full definition of a class template requires definitions for its function members and static data members Dynamic nonstatic data members are sufficiently defined by the class templ
34. cumentation server software from a Sun Web page For more information see Chapter 6 of Sun WorkShop Quick Install Accessing HTML Documents The following Sun Workshop documents are available online only in HTML format m Tools h Class Library Reference m Tools h User s Guide m Numerical Computation Guide xi m Standard C Library User s Guide m Standard C Class Library Reference m Sun WorkShop Performance Library Reference Manual m Sun WorkShop Visual User s Guide a Sun WorkShop Memory Monitor User s Manual To access these HTML documents 1 Open the following file through your HTML browser install directory SUNWspro DOC5 0 lib locale C html index html Replace install directory with the name of the directory where your Sun WorkShop software is installed the default is opt The browser displays an index of the HTML documents for the Sun WorkShop products that are installed 2 Open a document in the index by clicking the document s title Accessing Sun WorkShop Online Help and Release Notes This release of Sun WorkShop includes an online help system as well as online manuals To find out more see m Online Help A help system containing extensive task oriented context sensitive help To access the help choose Help Help Contents Help menus are available in all Sun WorkShop windows m Release Notes The Release Notes contain general information about Sun WorkShop and specific information about sof
35. definitions is to keep the definitions in template definition files as shown in the following example template lt class Number gt Number twice Number original twice h template lt class Number gt Number twice Number original return original original twice cc include twice h int main return twice lt int gt 3 Template definition files must not include any non idempotent header files and often need not include any header files at all See Idempotent Header Files on page 9 Note Although it is common to use source file extensions for template definition files c C cc cpp cxx template definition files are header files The compiler includes them automatically if necessary Template definition files should not be compiled independently If you place template declarations in one file and template definitions in another file you have to be very careful how you construct the definition file what you name it and where you put it You might also need to identify explicitly to the compiler the 10 C Programming Guide Revision A February 1999 location of the definitions Refer to C User s Guide for information about the template definition search rules Program Organization 11 12 C Programming Guide Revision A February 1999 CHAPTER 3 Pragmas This chapter describes pragmas A pragma is a compiler directive that allows the you to provide additional information
36. e for additional information on the variations between languages and versions To make header files acceptable to all these standards you might need to use conditional compilation based on the existence or value of the preprocessor macros __STDC__ and ___cplusplus The macro __STDC_ _ is not defined in K amp R C but is defined in both ANSI C and C Use this macro to separate K amp R C code from ANSI C or C code This macro is most useful for separating prototyped from nonprototyped function definitions ifdef STDC_ int function char 4 C amp ANSI C declaration else int function K amp R C endif The macro __cplusplus is not defined in C but is defined in C Note Early versions of C defined the macro c_plusplus instead of _cplusplus The macro c_plusplus is no longer defined Use the definition of the __cplusplus macro to separate C and C This macro is most useful in guarding the specification of an extern C interface for function declarations as shown in the following example To prevent inconsistent specification of extern C never place an include directive within the scope of an extern C linkage specification include header h ni other include files if defined _ _cplusplus extern C endif int g1 int g2 int g3 if define i i d _ _cplusplus endif In ARM C the _ _cplusplus macro has a value of 1 In ISO C the macro ha
37. e with C C programmers can learn C at their own pace and incorporate features of the new language when it seems appropriate C supplements what is good and useful about C Most important Introduction 3 C retains C s efficient interface to the hardware of the computer including types and operators that correspond directly to components of computing equipment C does have some important differences An ordinary C program might not be accepted by the C compiler without some modifications See the C Migration Guide for information about what you must know to move from programming in C to programming in C The differences between C and C are most evident in the way you can design interfaces between program modules but C retains all of C s facilities for designing such interfaces You can for example link C modules to C modules so you can use C libraries with C programs C differs from C in a number of other details In C m Typed constants allow you to avoid the preprocessor and use named constants in your program Function prototypes are required m The free store operators new and delete create dynamic objects of a specified type m References are automatically dereferenced pointers and act like alternate names for a variable You can use references as function parameters m Special built in operator names for type coercion are provided m Programmer defined automatic type conversion is allowed
38. ect file for the following example it generates an undefined error for the operator lt lt function which is not instantiated array h generates undefined error for the operator lt lt function ifndef ARRAY_H define ARRAY_H include lt iosfwd gt template lt class T gt class array int size public array friend std ostream amp operator lt lt std ostream amp const array lt T gt amp Templates 29 30 endif array cc include lt stdlib h gt include lt iostream gt template lt class T gt array lt T gt array size 1024 template lt class T gt std ostream amp operator lt lt std ostream amp out const array lt T gt amp rhs return out lt lt lt lt rhs size lt lt main cc include lt iostream gt include array h int main std scout lt lt creating an array of int lt lt std flush array lt int gt foo std cout lt lt done n std cout lt lt foo lt lt std endl return 0 Note that there is no error message during compilation because the compiler reads the following as the declaration of a normal function that is a friend of the array class friend ostream amp operator lt lt ostream amp const array lt T gt amp j Because operator lt lt is really a template function you need to supply a template declaration for it ahead of the declaration of template class array However because operator lt l
39. ecution This execution improvement is particularly noticeable with small value classes such as complex numbers or probability values You can sometimes improve program efficiency by designing classes that are more likely to be passed directly than indirectly In compatibility mode compat 4 a class is passed indirectly if it has any of the following Performance 59 m A user defined constructor m A virtual function m A virtual base class m A base that is passed indirectly Anon static data member that is passed indirectly Otherwise the class is passed directly In standard mode compat 5 a class is passed indirectly if it has any of the following a A user defined copy constructor m A user defined destructor m A base that is passed indirectly Anon static data member that is passed indirectly Otherwise the class is passed directly Choosing to Pass Classes Directly To maximize the chance that a class will be passed directly a Use default constructors especially the default copy constructor where possible m Use the default destructor where possible The default destructor is not virtual therefore a class with a default destructor should generally not be a base class a Avoid virtual functions and virtual bases Passing Classes Directly on Various Processors Classes and unions passed directly by the C compiler are passed exactly as the C compiler would pass a struct or union However C structs and
40. erator provides a way to check the actual type of a pointer to a polymorphic class You can search with a text editor for all new style casts search for _cast whereas finding old style casts required syntactic analysis Otherwise the new casts all perform a subset of the casts allowed by the classic cast notation For example const_cast lt int gt v could be written int v The new casts simply categorize the variety of operations available to express your intent more clearly and allow the compiler to provide better checking The cast operators are always enabled in C 5 0 They cannot be disabled Const Cast The expression const_cast lt T gt v can be used to change the const or volatile qualifiers of pointers or references Among new style casts only const_cast lt gt can remove const qualifiers T must be a pointer reference or pointer to member type class A 51 52 public virtual void f int i extern const int A cimp extern const volatile int cvip extern int ip void use_of_ const _cast const A al const_cast lt A amp gt al f remove const al const_cast lt int A gt cimp 1 remove const ip const_cast lt int gt cvip remove const and volatile reinterpret_cast The expression reinterpret_cast lt T gt v changes the interpretation of the value of the expression v It can be used to convert between pointer and integer types between unrelated pointer types
41. ermination due to a destructor throwing an exception while another exception is still active is to design your program so that destructors do not need to throw exceptions Matching Exceptions With Handlers A handler type T matches a throw type E if any of the following is true is the same as E m Tis const or volatile of E E m Eis const or volatile of T m Tis ref of E or E is ref of T is a public base class of E m T and E are both pointer types and E can be converted to T by a standard pointer conversion Exception Handling 41 Throwing exceptions of reference or pointer types can result in a dangling pointer if the object pointed or referred to is destroyed before exception handling is complete When an object is thrown a copy of the object is always made through the copy constructor and the copy is passed to the catch block It is therefore safe to throw a local or temporary object While handlers of type X and X amp both match an exception of type X the semantics are different Using a handler with type X invokes the object s copy constructor again If the thrown object is of a type derived from the handler type the object is truncated Catching a class object by reference therefore usually executes faster Handlers for a try block are tried in the order of their appearance Handlers for a derived class or a pointer to a reference to a derived class must precede
42. es pays Les produits portant les marques SPARC sont bas s sur une architecture d velopp e par Sun Microsystems Inc TM Les utilisateurs d interfaces graphiques OPEN LOOK et Sun ont t d velopp s de Sun Microsystems Inc pour ses utilisateurs et licenci s Sun reconna t les efforts de pionniers de Xerox Corporation pour la recherche et le d veloppement du concept des interfaces d utilisation visuelle ou graphique pour l industrie de l informatique Sun d tient une licence non exclusive de Xerox sur l interface d utilisation graphique cette licence couvrant aussi les licenci s de Sun qui mettent en place les utilisateurs d interfaces graphiques OPEN LOOK et qui en outre se conforment aux licences crites de Sun CETTE PUBLICATION EST FOURNIE EN L ETAT SANS GARANTIE D AUCUNE SORTE NI EXPRESSE NI IMPLICITE Y COMPRIS ET SANS QUE CETTE LISTE NE SOIT LIMITATIVE DES GARANTIES CONCERNANT LA VALEUR MARCHANDE L APTITUDE DES PRODUITS A REPONDRE A UNE UTILISATION PARTICULIERE OU LE FAIT QU ILS NE SOIENT PAS CONTREFAISANTS DE PRODUITS DE TIERS 7 eo Adobe PostScript Please Recycle Contents Preface vii Introduction 1 The C Language 1 Data Abstraction 2 Object Oriented Features 2 Type Checking 2 Classes and Data Abstraction 3 Compatibility With C 3 Program Organization 5 Header Files 5 Language Adaptable Header Files 5 Idempotent Header Files 6 Self Contained Header Files 7 Unnecessary Header File Inclusion 7 Inline
43. f 2 between 1 and 128 valid values are 1 2 4 8 16 32 64 and 128 m variable is a global or static variable it cannot be a local variable or a class member variable a If the specified alignment is smaller than the default the default is used m The pragma line must appear before the declaration of the variables that it mentions otherwise it is ignored m Any variable mentioned on the pragma line but not declared in the code following the pragma line is ignored Variables in the following example are properly declared pragma align 64 aninteger astring astruct int aninteger static char astring 256 struct S int a char b astruct pragma init identifier identifier Use init to mark identifier as an initialization function Such functions are expected to be of type void to accept no arguments and to be called while constructing the memory image of the program at the start of execution Initializers in a shared object are executed during the operation that brings the shared object into memory either at program start up or during some dynamic loading operation such as dlopen The only ordering of calls to initialization functions is the order in which they are processed by the link editors both static and dynamic C Programming Guide Revision A February 1999 Within a source file the functions specified in pragma init are executed after the static constructors in that file You must declare
44. function call are large or complicated The compiler is particularly sensitive when the object for an inline member function call is itself the result of an inline function call To inline functions with complicated arguments simply compute the function arguments into local variables and then pass the variables to the function 58 Using Default Operators If a class definition does not declare a parameterless constructor a copy constructor a copy assignment operator or a destructor the compiler will implicitly declare them These are called default operators A C like struct has these default operators C Programming Guide Revision A February 1999 When the compiler builds a default operator it knows a great deal about the work that needs to be done and can produce very good code This code is often much faster than user written code because the compiler can take advantage of assembly level facilities while the programmer usually cannot So when the default operators do what is needed the program should not declare user defined versions of these operators Default operators are inline functions so do not use default operators when inline functions are inappropriate see the previous section Default operators cannot be virtual Otherwise default operators are appropriate when a The user written parameterless constructor would only call parameterless constructors for its base objects and member variables Primitive types effect
45. guides provide additional useful information m The Solaris Linker and Libraries Guide gives information on linking and libraries m The Solaris Programming Utilities Guide provides information for developers about the special built in programming tools available in the SunOS system Commercially Available Books The following is a partial list of available books on the C language Object Oriented Analysis and Design with Applications Second Edition Grady Booch Addison Wesley 1994 Thinking in C Bruce Eckel Prentice Hall 1995 The Annotated C Reference Manual Margaret A Ellis and Bjarne Stroustrup Addison Wesley 1990 Design Patterns Elements of Reusable Object Oriented Software Erich Gamma Richard Helm Ralph Johnson and John Vlissides Addison Wesley 1995 C Primer Third Edition Stanley B Lippman and Josee Lajoie Addison Wesley 1998 Effective C 50 Ways to Improve Your Programs and Designs Second Edition Scott Meyers Addison Wesley 1998 More Effective C 35 Ways to Improve Your Programs and Designs Scott Meyers Addison Wesley 1996 STL Tutorial and Reference Guide Programming with the Standard Template Library David R Musser and Atul Saini Addison Wesley 1996 C for C Programmers Ira Pohl Benjamin Cummings 1989 The C Programming Language Third Edition Bjarne Stroustrup Addison Wesley 1997 Ordering Sun Documents TM The SunDocs program provides more than 250 manuals
46. he Sun WorkShop Memory Monitor garbage collection and memory management tools Other Sun WorkShop Books The following books are part of the Sun Visual WorkShop C documentation package m Sun WorkShop Quick Install provides installation instructions m Sun WorkShop Installation and Licensing Reference provides supporting installation and licensing information m Sun Visual WorkShop C Overview gives a high level outline of the C package suite m Using Sun WorkShop gives information on performing development operations through Sun WorkShop m C User s Guide tells how to use the C compiler m Numerical Computation Guide details floating point computation numerical accuracy issues m Debugging a Program With dbx provides information on using dbx commands to debug a program a Analyzing Program Performance With Sun WorkShop describes the profiling tools the LoopTool LoopReport and LockLint utilities and use of the Sampling Analyzer to enhance program performance m Sun WorkShop TeamWare User s Guide describes how to use the Sun WorkShop TeamWare code management tools m Sun WorkShop Performance Library Reference Manual discusses the library of subroutines and functions to perform useful operations in computational linear algebra and Fourier transforms m Sun WorkShop Visual User s Guide describes how to use Visual to create C and Java graphical user interfaces Solaris Books The following Solaris manuals and
47. hese automatic conversions you can explicitly convert between types using type casts A related area involves overloaded function names In C you can give any number of functions the same name The compiler decides which function should be called by checking the types of the parameters to the function call If the correct function is not clear at compile time the compiler issues an ambiguity error C Programming Guide Revision A February 1999 Classes and Data Abstraction If you are a C programmer think of a class as an extension of the struct type A struct contains predefined data types for example char or int and might also contain other struct types C allows a struct type to have not only data types to store data but also operations to manipulate the data The C keyword class is analogous to struct in C As a matter of style many programmers use struct to mean a C compatible struct type and class to meana struct type that has C features not available in C C provides classes as a means for data abstraction You decide what types classes you want for your program data and then decide what operations each type needs In other words a C class is a user defined data type For example if you define a class BigNum which implements arithmetic for very large integers you can define the operator so that it has a meaning when used with objects in the class BigNum If in the following expression n1 and n2 are
48. hing Into and Out of try Blocks and Handlers 37 Nesting of Exceptions 37 Specifying Exceptions to Be Thrown 38 Specifying Runtime Errors 38 Modifying the terminate and unexpected Functions 39 set_terminate 39 set_unexpected 40 Calling the uncaught_exception Function 41 Matching Exceptions With Handlers 41 Checking Access Control in Exceptions 42 Enclosing Functions in try Blocks 42 Contents v Disabling Exceptions 43 Using Runtime Functions and Predefined Exceptions 43 Building Shared Libraries With Exceptions 45 Using Exceptions in a Multithreaded Environment 45 6 Runtime Type Identification 47 Static and Dynamic Types 47 RTTI Options 47 typeid Operator 48 type_info Class 48 7 Cast Operations 51 New Cast Operations 51 const_cast 51 reinterpret_cast 52 static_cast 53 Dynamic Casts 54 Casting Up the Hierarchy 54 Casting to void 54 Casting Down or Across the Hierarchy 54 8 Performance 57 Avoiding Temporary Objects 57 Using Inline Functions 58 Using Default Operators 58 Using Value Classes 59 Choosing to Pass Classes Directly 60 Passing Classes Directly on Various Processors 60 Cache Member Variables 61 Index 63 C Programming Guide Revision A February 1999 Preface This manual tells you how to use C 5 0 features to write more efficient programs Who Should Use This Book This manual is intended for programmers with a working knowledge of C and some understanding of the Solaris operating environment
49. id exception when given a null pointer type_info Class The class type_info describes type information generated by the typeid operator The primary functions provided by type_info are equality inequality before and name From lt typeinfo h gt the definition is class type_info public virtual type_info bool operator const type_info amp rhs const bool operator const type_info amp rhs const C Programming Guide Revision A February 1999 bool before const type_info amp rhs const const char name const private type_info const type_info amp rhs type_info amp operator const type_info amp rhs The before function compares two types relative to their implementation dependent collation order The name function returns an implementation defined null terminated multibyte string suitable for conversion and display The constructor is a private member function so you cannot create a variable of type type_info The only source of type_info objects is in the typeid operator Runtime Type Identification 49 50 C Programming Guide Revision A February 1999 CHAPTER T Cast Operations This chapter discusses the new cast operators in the recently approved C standard const_cast reinterpret_cast static_cast and dynamic_cast New Cast Operations The C standard defines new cast operations that provide finer control than previous cast operations The dynamic_cast lt gt op
50. in the C standard You can access this header only when Exception Handling 43 44 compiling in standard mode compiler default mode or with option compat 5 The header provides the following declarations standard header lt exception gt namespace std class exception exception throw exception const exception amp throw exception amp operator const exception amp throw virtual exception throw virtual const char what const throw class bad exception public exception Unexpected exception handling typedef void unexpected_handler unexpected_handler set_unexpected unexpected_handler throw void unexpected Termination handling typedef void terminate_handler terminate_handler set_terminate terminate_handler throw void terminate bool uncaught_exception throw The standard class exception is the base class for all exceptions thrown by selected language constructs or by the C standard library An object of type exception can be constructed copied and destroyed without generating an exception The virtual member function what returns a character string that describes the exception For compatibility with exceptions as used in C release 4 2 the header lt exception h gt is also provided for use in standard mode This header allows for a transition to standard C code and contains declarations that are not part of standard C Update your code t
51. ion handler has been entered the exception is considered handled and exceptions may be thrown again You can determine whether any exception has been thrown and is currently unhandled See Calling the uncaught_exception Function on page 41 Exception Handling 37 38 Specifying Exceptions to Be Thrown A function declaration can include an exception specification a list of exceptions that a function may throw directly or indirectly The two following declarations indicate to the caller that the function 1 generates only exceptions that can be caught by a handler of type X and that the function 2 generates only exceptions that can be caught by handlers of type w Y or Z void fl int throw X void f2 int throw W Y 2Z A variation on the previous example is void f3 int throw empty parentheses This declaration guarantees that no exception is generated by the function f3 If a function exits via any exception that is not allowed by an exception specification it results in a call to the predefined function unexpected By default unexpected calls abort to exit the program You can change this default behavior by calling the set_unexpected function See set_unexpected on page 40 n The check for unexpected exceptions is done at program execution time not at compile time Even if it appears that a disallowed exception might be thrown there is no error unless the disallowed exception is act
52. ively have do nothing parameterless constructors m The user written copy constructor would simply copy all base objects and member variables a The user written copy assignment operator would simply copy all base objects and member variables m The user written destructor would be empty Some C programming texts suggest that class programmers always define all operators so that any reader of the code will know that the class programmer did not forget to consider the semantics of the default operators Obviously this advice interferes with the optimization discussed above The resolution of the conflict is to place a comment in the code stating that the class is using the default operator Using Value Classes C classes including structures and unions are passed and returned by value For Plain Old Data POD classes the C compiler is required to pass the struct as would the C compiler Objects of these classes are passed directly For objects of classes with user defined copy constructors the compiler is effectively required to construct a copy of the object pass a pointer to the copy and destruct the copy after the return Objects of these classes are passed indirectly For classes that fall between these two requirements the compiler can choose However this choice affects binary compatibility so the compiler must choose consistently for every class For most compilers passing objects directly can result in faster ex
53. locks associated with the try block Whenever an exception is thrown and caught and control is returned outside of the function that threw the exception stack unwinding takes place During stack unwinding any automatic objects that were created within the scope of the block that was exited are safely destroyed via calls to their destructors If a try block ends without an exception all associated catch blocks are ignored Note An exception handler cannot return control to the source of the error by using the return statement A return issued in this context returns from the function containing the catch block Branching Into and Out of try Blocks and Handlers Branching out of a try block or a handler is allowed Branching into a catch block is not allowed however because that is equivalent to jumping past an initiation of the exception Nesting of Exceptions Nesting of exceptions that is throwing an exception while another remains unhandled is allowed only in restricted circumstances From the point when an exception is thrown to the point when the matching catch clause is entered the exception is unhandled Functions that are called along the way such as destructors of automatic objects being destroyed may throw new exceptions as long as the exception does not escape the function If a function exits via an exception while another exception remains unhandled the terminate function is called immediately Once an except
54. m formatting ios intro Introduces iostream man pages manip Provides iostream manipulators ostream Supports formatted and unformatted output queue Provides list management for task library sbufprot Provides protected interface of streambuffer base class sbufpub Provides public interface of streambuffer base class xiii xiv TABLE P 1 C Man Pages continued Title sigfpe ssbuf stdarg stdiobuf stream_locker stream_MT strstream varargs vector Description Allows signal handling for specific SIGFPE codes Provides buffer class for character arrays Handles variable argument list Provides buffer and stream classes for use with C stdio Provides class used for application level locking of iostream class object Base class that provides dynamic changing of iostream class object to and from MT safely Provides stream class for I O using character arrays Handles variable argument list Provides generic vector and stack Table P 2 lists man pages that contain information related to the C compiler TABLE P 2 Man Pages Related to C Title c filt dem fbe fpversion gprof ild inline Description Copies each file name in sequence and writes it in the standard output after decoding symbols that look like C demangled names Demangles one or more C names that you specify Creates object files from assembly language source files Prints information about the system CPU and FPU Produces execution
55. mes a template definition uses names that are not defined by the template arguments or Within the template itself If so the compiler resolves the name from the scope enclosing the template which could be the context at the point of definition or at the point of instantiation A name can have different meanings in different places yielding different resolutions Name resolution is complex Consequently you should not rely on nonlocal names except those provided in a pervasive global environment That is use only nonlocal names that are declared and mean the same thing everywhere In the following example the template function converter uses the nonlocal names intermediary and temporary These names have different definitions in use1 cc and use2 cc and will probably yield different results under different compilers For templates to work reliably all nonlocal names intermediary and temporary in this case must have the same definition everywhere use_common h Common template definition template lt class Source class Target gt Target converter Source source temporary intermediary source return Target temporary usel cc typedef int intermediary int temporary include use_common h use2 cc typedef double intermediary unsigned int temporary include use_common h A common use of nonlocal names is the use of the cin and cout streams within a template Few programmers really want to pass the stream as
56. mplate keyword by a declaration not definition for the class with the class identifier followed by the template arguments template class Array lt char gt template class String lt 19 gt When you explicitly instantiate a class all of its members are also instantiated For Template Class Function Members To explicitly instantiate a template class function member follow the template keyword by a declaration not definition for the function with the function identifier qualified by the template class followed by the template arguments template int Array lt char gt GetSize template int String lt 19 gt length For Template Class Static Data Members To explicitly instantiate a template class static data member follow the template keyword by a declaration not definition for the member with the member identifier qualified by the template class followed by the template argument template int String lt 19 gt overflow Template Composition You can use but not define templates in a nested manner This is particularly useful when defining generic functions over generic data structures as in the standard C library For example a template sort function may be declared over a template array class template lt class Elem gt void sort Array lt Elem gt Templates 25 26 and defined as template lt class Elem gt void sort Array lt Elem gt store int num elems store GetSize for int
57. n the following example any exception thrown from the constructor of base class B or member e is caught before the body of the T constructor is entered and is handled by the matching catch block You cannot use a return statement in the handler of a function try block because the catch block is outside the function You can only throw an exception or terminate the program by calling exit or terminate class B class E class T public B public T private E e Te3T try B args E args body of constructor catch X amp x handle exception X Sateh t 2359 handle any other exception Disabling Exceptions If you know that exceptions are not used in a program you can use the compiler option features no except to suppress generation of code that supports exception handling The use of the option results in slightly smaller code size and faster code execution However when files compiled with exceptions disabled are linked to files using exceptions some local objects in the files compiled with exceptions disabled are not destroyed when exceptions occur By default the compiler generates code to support exception handling Unless the time and space overhead is important it is usually better to leave exceptions enabled Using Runtime Functions and Predefined Exceptions The standard header lt exception gt provides the classes and exception related functions specified
58. nts template lt unsigned Size gt int String lt Size gt overflows 0 Class Template Use A template class can be used wherever a type can be used Specifying a template class consists of providing the values for the template name and arguments The declaration in the following example creates the variable int_array based upon the Array template The variable s class declaration and its set of methods are just like those in the Array template except that Elem is replaced with int see Template Instantiation on page 23 Array lt int gt int_array 100 The declaration in this example creates the short_string variable using the String template String lt 8 gt short_string hello You can use template class member functions as you would any other member function int x int_array GetSize int x short_string length Template Instantiation Template instantiation involves generating a concrete class or function instance for a particular combination of template arguments For example the compiler generates a class for Array lt int gt and a different class for Array lt double gt The new classes are defined by substituting the template arguments for the template parameters in the Templates 23 definition of the template class In the Array lt int gt example shown in the preceding Class Templates section the compiler substitutes int wherever Elem appears Implicit Template Instan
59. o follow the C standard using lt exception gt instead of lt exception h gt as development schedules permit header lt exception h gt used for transition include lt exception gt include lt new gt using std exception using std bad_exception using std set_unexpected using std unexpected using std set_terminate using std terminate typedef std exception xmsg typedef std bad_exception xunexpected typedef std bad_alloc xalloc In compatibility mode option compat 4 header lt exception gt is not available and header lt exception h gt refers to the same header provided with C release 4 2 It is not reproduced here C Programming Guide Revision A February 1999 Building Shared Libraries With Exceptions When shared libraries are opened with dlopen you must use RTLD_ GLOBAL for exceptions to work Note When building shared libraries with exceptions in them do not pass the option Bsymbolic to ld Exceptions that should be caught might be missed Using Exceptions in a Multithreaded Environment The current exception handling implementation is safe for multithreading exceptions in one thread do not interfere with exceptions in other threads However you cannot use exceptions to communicate across threads an exception thrown from one thread cannot be caught in another Each thread can set its own terminate or unexpected function Calling set_terminate or set_unexpected
60. ombination of template arguments The following examples declare specialized implementations of twice and sort template lt gt unsigned twice lt unsigned gt unsigned original template lt gt sort lt char gt Array lt char gt store You can omit the template arguments if the compiler can unambiguously determine them For example template lt gt unsigned twice unsigned original template lt gt sort Array lt char gt store Template Specialization Definition You must define all template specializations that you declare The following examples define the functions declared in the preceding section template lt gt unsigned twice lt unsigned gt unsigned original return original lt lt 1 include lt string h gt template lt gt void sort lt char gt Array lt char gt store int num_elems store GetSize fore Ente av 0 i lt num_elems 1 itt for int j itl j lt num_elems j if stremp store j 1 store j gt 0 char temp store j store j store j 1 store j 1 temp Template Specialization Use and Instantiation A specialization is used and instantiated just as any other template except that the definition of a completely specialized template is also an instantiation Templates 27 28 Template Problem Areas This section describes problems you might encounter when using templates Nonlocal Name Resolution and Instantiation Someti
61. plemented inline The disadvantage is that this organization repeats the prototype of the class which increases the bulk of source files and the chance for inconsistencies Template Definitions You can organize your template definitions in two ways with definitions included and with definitions separated The definitions included organization allows greater control over template compilation Definitions Included When you put the declarations and definitions for a template within the file that uses the template the organization is definitions included For example Program Organization 9 template lt class Number gt Number twice Number original template lt class Number gt Number twice Number original return original original int main return twice lt int gt 3 When a file using a template includes a file that contains both the template s declaration and the template s definition the file that uses the template also has the definitions included organization For example ifndef TWICE_H define TWICE_H template lt class Number gt Number twice Number original template lt class Number gt Number twice Number original return original original endif include twice h int main return twice 3 Note It is very important to make your template headers idempotent See Idempotent Header Files on page 9 Definitions Separate Another way to organize template
62. processors and compatible microprocessor chips made by AMD and Cyrix In this document the term x86 refers to the overall platform architecture Features described in this book that are particular to a specific platform are differentiated by the terms SPARC and x86 in the text viii C Compiler Related Books The following books are part of the C 5 0 documentation package m C User s Guide instructs you in the use of the C 5 0 compiler and provides detailed information on command line options m C Library Reference describes the C libraries including the C Standard Library the Tools h Class Library the Sun WorkShop Memory Monitor and the iostream and complex libraries m C Migration Guide explains what you need to know when moving from 4 0 4 0 1 4 1 or 4 2 versions of the C compiler to the C 5 0 version m Tools h User s Guide discusses use of the C classes for enhancing the efficiency of your programs m Tools h Class Library Reference provides details on the Tools h class library C Programming Guide Revision A February 1999 m C Standard Library 2 0 User s Guide instructs you in the use of the C Standard Library including locales and iostreams m C Standard Library Class Reference provides more detailed information on the use of the C Standard Library m Sun WorkShop Memory Monitor User s Guide describes how to use t
63. produce an exception in a try block m Code one or more catch blocks immediately after the try block Each catch block identifies what type or class of objects it is capable of catching When an object is thrown by the exception this is what takes place Exception Handling 35 a If the object thrown by the exception matches the type of the catch expression control passes to that catch block a If the object thrown by the exception does not match the first catch block subsequent catch blocks are searched for a matching type a If try blocks are nested and there is no match control passes from the innermost catch block to the nearest catch block surrounding the try block a Ifno matching catch block is found in the current function any automatic local nonstatic objects in the current function are destroyed and the function exits immediately A search for a matching catch block continues with the function that called the current function This process continues up to function main a If there is no match in any of the catch blocks the program is normally terminated with a call to the predefined function terminate By default terminate calls abort which destroys all remaining objects and exits from the program This default behavior can be changed by calling the set_terminate function Synchronous Exception Handling Exception handling is designed to support only synchronous exceptions such as array range checks The te
64. races whose purpose is to handle the exception 34 C Programming Guide Revision A February 1999 throw The throw statement is used to throw an exception and its value to a subsequent exception handler A regular throw consists of the keyword throw and an expression The result type of the expression determines which catch block receives control Within a catch block the current exception and value may be re thrown simply by specifying the throw keyword alone with no expression In the following example the function call in the try block passes control to f which throws an exception of type Overflow This exception is handled by the catch block which handles type Overflow exceptions class Overflow FRET public Overflow char double double void f double x ARRETE throw Overflow x 3 45e107 int main try TA seer 1 2 i fen catch Overflows oo handle exceptions of type Overflow here Implementing Exception Handlers To implement an exception handler do these basic tasks m When a function is called by many other functions code it so that an exception is thrown whenever an error is detected The throw expression throws an object This object is used to identify the types of exceptions and to pass specific information about the exception that has been thrown m Use the try statement in a client program to anticipate exceptions Enclose function calls that might
65. rm synchronous exception means that exceptions can only be originated from throw expressions The C standard supports synchronous exception handling with a termination model Termination means that once an exception is thrown control never returns to the throw point Asynchronous Exception Handling Exception handling is not designed to directly handle asynchronous exceptions such as keyboard interrupts However you can make exception handling work in the presence of asynchronous events if you are careful For instance to make exception handling work with signals you can write a signal handler that sets a global variable and create another routine that polls the value of that variable at regular intervals and throws an exception when the value changes Managing Flow of Control In C exception handlers do not correct the exception and then return to the point at which the exception occurred Instead when an exception is generated control is 36 C Programming Guide Revision A February 1999 passed out of the block that threw the exception out of the try block that anticipated the exception and into the catch block whose exception declaration matches the exception thrown The catch block handles the exception It might rethrow the same exception throw another exception jump to a label return from the function or end normally If a catch block ends normally without a throw the flow of control passes over all other catch b
66. rwise use inline functions when the code to expand the function inline is smaller than the code to call the function or the application performs significantly faster with the function inline The compiler cannot inline all function calls so making the most effective use of function inlining may require some source changes Use the w option to learn when function inlining does not occur In the following situations the compiler will not inline the function m The function contains difficult control constructs such as loops switch statements and try catch statements Many times these functions execute the difficult control constructs infrequently To inline such a function split the function into two parts an inner part that contains the difficult control constructs and an outer part that decides whether or not to call the inner part This technique of separating the infrequent part from the frequent part of a function can improve performance even when the compiler can inline the full function m The inline function body is large or complicated Apparently simple function bodies may be complicated because of calls to other inline functions within the body or because of implicit constructor and destructor calls as often occurs in constructors and destructors for derived classes For such functions inline expansion rarely provides significant performance improvement and the function is best left uninlined m The arguments to an inline
67. s the value 199711L the year and month of the standard expressed as a long constant Use the value of this macro to separate ARM C from ISO C The macro value is most useful for guarding changes in template syntax template function specialization if _ _cplusplus lt 199711L int power int int ARM C else template lt gt int power int int ISO C endif Idempotent Header Files Your header files should be idempotent That is the effect of including a header file many times should be exactly the same as including the header file only once This property is especially important for templates You can best accomplish idempotency C Programming Guide Revision A February 1999 by setting preprocessor conditions that prevent the body of your header file from appearing more than once ifndef HEADER _H define HEADER _H contents of header file endif Self Contained Header Files Your header files should include all the definitions that they need to be fully compilable Make your header file self contained by including within it all header files that contain needed definitions include another h definitions that depend on another h In general your header files should be both idempotent and self contained ifndef HEADER_H define HEADER_H include another h definitions that depend on another h endif Unnecessary Header File Inclusion Programs writ
68. s C Sun WorkShop Compilers C Sun WorkShop Compilers Fortran Sun WorkShop Memory Monitor Sun WorkShop Professional Sun WorkShop Professional C and Sun WorkShop TeamWare are trademarks registered trademarks or service marks of Sun Microsystems Inc in the U S and other countries All SPARC trademarks are used under license and are trademarks or registered trademarks of SPARC International Inc in the U S and other countries Products bearing SPARC trademarks are based upon an architecture developed by Sun Microsystems Inc The OPEN LOOK and Sun Graphical User Interfaces were developed by Sun Microsystems Inc for its users and licensees Sun acknowledges the pioneering efforts of Xerox Corporation in researching and developing the concept of visual or graphical user interfaces for the computer industry Sun holds a nonexclusive license from Xerox to the Xerox Graphical User Interface which license also covers Sun s licensees who implement OPEN LOOK GUIs and otherwise comply with Sun s written license agreements THIS PUBLICATION IS PROVIDED AS IS WITHOUT WARRANTY OF ANY KIND EITHER EXPRESS OR IMPLIED INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY FITNESS FOR A PARTICULAR PURPOSE OR NON INFRINGEMENT Copyright 1999 Sun Microsystems Inc 901 San Antonio Road Palo Alto Californie 94303 4900 U S A Tous droits r serv s Ce produit ou document est prot g par un copyright et distribu avec de
69. s licences qui en restreignent l utilisation la copie et la d compilation Aucune partie de ce produit ou de sa documentation associ e ne peut tre reproduite sous aucune forme par quelque moyen que ce soit sans l autorisation pr alable et crite de Sun et de ses bailleurs de licence s il y en a Des parties de ce produit pourront tre deriv es du syst me UNIX licenci par Novell Inc et du syst me Berkeley 4 3 BSD licenci par l Universit de Californie UNIX est une marque enregistr e aux Etats Unis et dans d autres pays et licenci e exclusivement par X Open Company Ltd Le logiciel d tenu par des tiers et qui comprend la technologie relative aux polices de caract res est prot g par un copyright et licenci par des fournisseurs de Sun Sun Sun Microsystems the Sun logo SunDocs SunExpress Solaris Sun Performance Library Sun Performance WorkShop Sun Performance WorkShop Fortran Sun Visual WorkShop Sun WorkShop Sun WorkShop Compilers C Sun WorkShop Compilers C Sun WorkShop Compilers Fortran Sun WorkShop Memory Monitor Sun WorkShop Professional Sun WorkShop Professional C et Sun WorkShop TeamWare sont des marques de fabrique ou des marques d pos es ou marques de service de Sun Microsystems Inc aux Etats Unis et dans d autres pays Toutes les marques SPARC sont utilis es sous licence et sont des marques de fabrique ou des marques d pos es de SPARC International Inc aux Etats Unis et dans d autr
70. s to be emphasized Example Edit your login file Use 1s a to list all files machine_name You have mail machine_name su Password To delete a file type rm filename Read Chapter 6 in User s Guide These are called class options You must be root to do this Compiler options and commands use the following conventions O oe lt gt Square brackets contain arguments that are optional Parentheses contain a set of choices for a required option The pipe or bar symbol separates arguments only one of which may be used at one time The ellipsis indicates omission in a series The percent sign indicates the word has a special meaning In ASCII files such as the README file angle brackets contain a variable that must be replaced by an appropriate value xvi C Programming Guide Revision A February 1999 xO n d yln d y In xinline fI fn ftrap all no division xtemp lt dir gt Shell Prompts in Command Examples The following table shows the default system prompt and superuser prompt for the C shell Bourne shell and Korn shell TABLE P 4 System Prompts Shell C shell prompt C shell superuser prompt Bourne shell and Korn shell prompt Bourne shell and Korn shell superuser prompt Prompt machine_name machine_name xviii C Programming Guide Revision A February 1999 CHAPTER 1 Introduction The Sun C compiler CC
71. sses only those performance techniques that strongly affect the Sun C compiler Avoiding Temporary Objects C functions often produce many implicit temporary objects each of which must be created and destroyed For non trivial classes this creation and destruction can get expensive The Sun C compiler does eliminate some temporary objects but it cannot eliminate all of them Write functions to minimize the number of temporary objects as long as your programs remain comprehensible Techniques include using explicit variables rather than implicit temporary objects and using reference parameters rather than value parameters Another technique is to implement and use operations such as rather than implementing and using only and For example the first line below introduces a temporary object for the result of a b while the second line does not Tx atb T x a x b 57 Using Inline Functions Calls to small and quick functions can be smaller and quicker when expanded inline than when called normally Conversely calls to large or slow functions can be larger and slower when expanded inline than when branched to Furthermore all calls to an inline function must be recompiled whenever the function definition changes Consequently the decision to use inline functions requires considerable care Do not use inline functions when you anticipate changes to the function definition and recompiling all callers is expensive Othe
72. t has a parameter of type array lt T gt you must precede the function declaration with a declaration of array lt T gt The file array h must look like this ifndef ARRAY_H define ARRAY_H include lt iosfwd gt the next two lines declare operator lt lt as a template function template lt class T gt class array template lt class T gt std ostream amp operator lt lt std ostream amp const array lt T gt amp template lt class T gt class array int size public array friend std ostream amp operator lt lt std ostream amp const array lt T gt amp endif C Programming Guide Revision A February 1999 Using Qualified Names Within Template Definitions The C standard requires types with qualified names that depend upon template arguments to be explicitly noted as type names with the typename keyword This is true even if the compiler can know that it should be a type The comments in the following example show the types with qualified names that require the typename keyword struct simple typedef int a_ type static int a_datum int simple a_datum 0 not a type template lt class T gt struct parametric typedef T a_type static T a_datum template lt class T gt T parametric lt T gt a_datum 0 not a type template lt class T gt struct example static typename T a_type variablel dependent static typename parametric lt T gt a_type variable2
73. ten in C typically include many more declarations than do C programs resulting in longer compilation times You can reduce the number of declarations through judicious use of several techniques One technique is to conditionally include the header file itself using the macro defined to make it idempotent This approach introduces an additional interfile dependence ifndef HEADER H include header h endif Program Organization 7 Note System header files often include guards of the form _Xxxx where X is an uppercase letter These identifiers are reserved and should not be used as a model for constructing macro guard identifiers Another way to reduce compilation time is to use incomplete class and structure declarations rather than including a header file that contains the definitions This technique is applicable only if the complete definition is not needed and if the identifier is actually a class or structure and not a typedef or template The standard library has many typedefs that are actually templates and not classes For example rather than writing include class h a_class a_ptr write class a_class a_class a_ptr If a_class is really a typedef the technique does not work One other technique is to use interface classes and factories as described in the book Design Patterns Elements of Reusable Object Oriented Software by Erich Gamma Addison Wesley 1994 Inline Function
74. the user for another file to try or shut down the program gracefully Without exception handlers status and data would have to be passed down and up the function call hierarchy with status checks after every function call With exception handlers the flow of control is not obscured by error checking If a function returns the caller can be certain that it succeeded Exception handlers have disadvantages If a function does not return because it or some other function it called threw an exception data might be left in an inconsistent state You need to know when an exception might be thrown and whether the exception might have a bad effect on the program state Using Exception Handling Keywords There are three keywords for exception handling in C Em try m catch m throw try A try block is a group of C statements normally enclosed in braces which might cause an exception This grouping restricts exception handlers to exceptions generated within the try block Each try block has one or more associated catch blocks catch A catch block is a group of C statements that are used to handle a specific thrown exception One or more catch blocks or handlers should be placed after each try block A catch block is specified by m The keyword catch m A catch parameter enclosed in parentheses which corresponds to a specific type of exception that may be thrown by the try block m A group of statements enclosed in b
75. tiation The use of a template function or template class introduces the need for an instance If that instance does not already exist the compiler implicitly instantiates the template for that combination of template arguments Whole Class Instantiation When the compiler implicitly instantiates a template class it usually instantiates only the members that are used To force the compiler to instantiate all member functions when implicitly instantiating a class use the template wholeclass compiler option To turn this option off specify the template no wholeclass option which is the default Explicit Template Instantiation The compiler implicitly instantiates templates only for those combinations of template arguments that are actually used This approach may be inappropriate for the construction of libraries that provide templates C provides a facility to explicitly instantiate templates as seen in the following examples For Template Functions To instantiate a template function explicitly follow the template keyword by a declaration not definition for the function with the function identifier followed by the template arguments template float twice lt float gt float original Template arguments may be omitted when the compiler can infer them template int twice int original 24 C Programming Guide Revision A February 1999 For Template Classes To instantiate a template class explicitly follow the te
76. to the compiler This information can change compilation details that are not otherwise under your control For example the pack pragma affects the layout of data within a structure Compiler pragmas are also called directives Pragma Forms Note Pragmas are not part of any C standard The various forms of a CC pragma are pragma keyword pragma keyword al a 1 keyword a a yn pragma sun keyword The variable keyword identifies the specific directive a indicates an argument The pragma keywords recognized by CC are m align Makes the parameter variables memory aligned to a specified number of bytes overriding the default m init Marks a specified function as an initialization function m fini Marks a specified function as a finalization function 13 14 m ident Places a specified string in the comment section of the executable m pack n Controls the layout of structure offsets The value of n is a number 0 1 2 4 or 8 that specifies the worst case alignment desired for any structure member m unknown_control_flow Specifies a list of routines that violate the usual control flow properties of procedure calls m weak Defines weak symbol bindings Pragma Reference pragma align integer variable variable Use align to make the listed variables memory aligned to integer bytes overriding the default The following limitations apply m integer must be a power o
77. tware limitations and bugs To access the Release Notes choose Help Release Notes Man Pages Online man pages provide immediate documentation about a command or library function You can display a man page by running the command demo man topic Man pages are in opt install dir SUNWspro man Table P 1 lists and describes the C man pages xii C Programming Guide Revision A February 1999 Note Before you use the man command at the beginning of your search path insert the name of the directory in which you have chosen to install the C compiler This enables you to use the man command This is usually done in the cshrc file in a line with setenv MANPATH at the start or in the profile file ina line with export MANPATH at the start TABLE P 1 C Man Pages Title Description CC Drives the C compilation system cartpol Provides Cartesian polar functions in the C complex number math library cplx intro Introduces the C complex number math library cplxerr Provides complex error handling functions in the C complex number math library cplxops Provides arithmetic operator functions in the C complex number math library cplextrig Provides trigonometric operator functions in the C complex number math library demangle Decodes a C encoded symbol name filebuf Buffer class for file I O fstream Provides stream class for file 1 0 istream Supports formatted and unformatted input ios Provides basic iostrea
78. twice Number original return original original Because template definitions often appear in header files a template definition might be repeated in several compilation units All definitions however must be the same This restriction is called the One Definition Rule C 5 0 does not support non type template parameters for function templates For example the following template is not supported because its argument is an expression instead of a type template lt int count gt void foo unsupported non type parameter int x count for int i 0 i lt count i do something with x foo lt 10 gt call foo with template argument 10 unsupported Function Template Use Once declared templates can be used like any other function Their use consists of naming the template and providing function arguments The compiler infers the template type arguments from the function argument types For example you can use the previously declared template as follows double twicedouble double item return twice item C Programming Guide Revision A February 1999 Class Templates A class template describes a set of related classes or data types that differ only by types by integral values by pointers or references to variables with global linkage or by a combination thereof Class templates are particularly useful in describing generic but type safe data structures Class Template Declar
79. ually thrown at runtime The compiler can however eliminate unnecessary checking in some simple cases For instance no checking for f is generated in the following example void foo int throw x void f int throw x foo 13 The absence of an exception specification allows any exception to be thrown Specifying Runtime Errors There are five runtime error messages associated with exceptions m No handler for the exception m Unexpected exception thrown C Programming Guide Revision A February 1999 m An exception can only be re thrown in a handler m During stack unwinding a destructor must handle its own exception m Out of memory When errors are detected at runtime the error message displays the type of the current exception and one of the five error messages By default the predefined function terminate is called which then calls abort The compiler uses the information provided in the exception specification to optimize code production For example table entries for functions that do not throw exceptions are suppressed and runtime checking for exception specifications of functions is eliminated wherever possible Thus declaring functions with correct exception specifications can lead to better code generation Modifying the terminate and unexpected Functions The following sections describe how to modify the behavior of the terminate and unexpected functions using set_terminate and set_
80. unction succeeds void simple dynamic _casts AB ab B bp B amp ab cast needed to break protection A ap amp ab public derivation no cast needed AB amp abr dynamic _cast lt AB amp gt bp succeeds ap dynamic_cast lt A gt bp assert ap NULL bp dynamic_cast lt B gt ap assert bp NULL ap dynamic_cast lt A gt amp abr assert ap NULL bp dynamic_cast lt B gt amp abr assert bp NULL In the presence of virtual inheritance and multiple inheritance of a single base class the actual dynamic cast must be able to identify a unique match If the match is not unique the cast fails For example given the additional class definitions class ABB public AB public B class AB_B AB public AB_B public AB The following function succeeds void complex_dynamic_casts AB_B_ AB ab_b_ ab A ap amp ab_b_ ab okay finds unique A statically AB abp dynamic_cast lt AB gt ap fails ambiguous assert abp NULL STATIC ERROR AB_B ab_bp AB_B ap not a dynamic cast AB_B ab_bp dynamic_cast lt AB_B gt ap dynamic one is okay assert ab_bp NULL The null pointer error return of dynamic_cast is useful as a condition between two bodies of code one to handle the cast if the type guess is correct and one if it is not Cast Operations 55 void using_dynamic_cast A ap if AB abp dynamic_cast lt AB gt
81. unexpected set _terminate You can modify the default behavior of terminate by calling the function set_terminate as shown in the following example declarations are in standard header lt exception gt namespace std typedef void terminate_handler terminate_handler set_terminate terminate_handler f throw void terminate The terminate function is called in any of the following circumstances m The exception handling mechanism calls a user function including destructors for automatic objects that exits via an uncaught exception while another exception remains uncaught m The exception handling mechanism cannot find a handler for a thrown exception m The construction or destruction of a nonlocal object with static storage duration exits using an exception Exception Handling 39 m Execution of a function registered with atexit exits using an exception m A throw expression with no operand attempts to rethrow an exception and no exception is being handled m The unexpected function throws an exception that is not allowed by the previously violated exception specification and std bad_exception is not included in that exception specification m The default version of unexpected is called The terminate function calls the function passed as an argument to set_terminate Such a function takes no parameters returns no value and must terminate the program or the current thread The

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