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Chapter 3

Sun ANSI/ISO C Compiler-Specific Information

The Sun ANSI/ISO C compiler is compatible with the C language described in the American National Standard for Programming Language--C, ANSI/ISO 9899-1990. This chapter documents those areas specific to the Sun ANSI/ISO C compiler and is organized into the following sections:

Environment Variables

TMPDIR

cc normally creates temporary files in the directory /tmp. You can specify another directory by setting the environment variable TMPDIR to the directory of your choice. However, if TMPDIR is not a valid directory, cc uses /tmp. The -xtemp option has precedence over the TMPDIR environment variable.

If you use a Bourne shell, type:

$ TMPDIR=dir; export TMPDIR


If you use a C shell, type:

% setenv TMPDIR dir


SUNPRO_SB_INIT_FILE_NAME

The absolute path name of the directory containing the .sbinit(5) file. This variable is used only if the -xsb or -xsbfast flag is used.

PARALLEL

(SPARC) Specifies the number of processors available to the program for multiprocessor execution. If the target machine has multiple processors, the threads can map to independent processors. Running the program leads to the creation of two threads that execute the parallelized portions of the program.

SUNW_MP_THR_IDLE

Controls the status of each thread after it finishes its share of a parallel job. You can set SUNW_MP_THR_IDLE to either spin or sleep [n s|n ms]. The default is spin, which means the thread goes spin-waiting. The other choice, sleep [n s|n ms] puts the thread to sleep after spin-waiting for n units. The wait can be seconds (s is the default unit) or milliseconds (ms) where 1s means one second, 10 ms means ten milliseconds. If a new job arrives before n units is reached, the thread stops spin-waiting and starts doing the new job. If SUNW_MP_THR_IDLE contains an illegal value or is not set, spin is used as the default.

Global Behavior: Value Versus unsigned Preserving

A program that depends on unsigned preserving arithmetic conversions behaves differently. This is considered to be the most serious change made by ANSI/ISO C.

In the first edition of K&R, The C Programming Language (Prentice-Hall, 1978), unsigned specified exactly one type; there were no unsigned chars, unsigned shorts, or unsigned longs, but most C compilers added these very soon thereafter.

In K&R C compilers, the unsigned preserving rule is used for promotions: when an unsigned type needs to be widened, it is widened to an unsigned type; when an unsigned type mixes with a signed type, the result is an unsigned type.

The other rule, specified by ANSI/ISO C, came to be called "value preserving," in which the result type depends on the relative sizes of the operand types. When an unsigned char or unsigned short is widened, the result type is int if an int is large enough to represent all the values of the smaller type. Otherwise, the result type is unsigned int. The value preserving rule produces the least surprise arithmetic result for most expressions.

Only in the -Xt and -Xs modes does the compiler use the unsigned preserving promotions; in the other modes, -Xc and -Xa, the value preserving promotion rules are used. When the -xtransition option is used, the compiler warns about each expression whose behavior might depend on the promotion rules used.

Keywords

asm Keyword

The _asm keyword is a synonym for the asm keyword. asm is available under all compilation modes except the -Xc mode.The asm statement has the form:

asm("string");

where string is a valid assembly language statement. The asm statements must appear within function bodies.

_Restrict Keyword

For a compiler to effectively perform parallel execution of a loop, it needs to determine if certain lvalues designate distinct regions of storage. Aliases are lvalues whose regions of storage are not distinct. Determining if two pointers to objects are aliases is a difficult and time-consuming process because it could require analysis of the entire program.

For example, consider the functions vsq():

void vsq(int n, double * a, double * b)

{

	 int i;

	 for (i=0; i<n; i++) b[i] = a[i] * a[i];

}


The compiler can parallelize the execution of the different iterations of the loops if it knows that pointers a and b access different objects. If there is an overlap in objects accessed through pointers a and b then it would be unsafe for the compiler to execute the loops in parallel. At compile time, the compiler does not know if the objects accessed by a and b overlap by simply analyzing the function vsq(); the compiler may need to analyze the whole program to get this information.

Restricted pointers are used to specify pointers which designate distinct objects so that the compiler can perform pointer alias analysis. To support restricted pointers, the keyword _Restrict is recognized by the Sun ANSI/ISO C compiler as an extension. Below is an example of declaring function parameters of vsq() as restricted pointers:

void vsq(int n, double * _Restrict a, double * _Restrict b)


Pointers a and b are declared as restricted pointers, so the compiler knows that the regions of storage pointed to by a and b are distinct. With this alias information, the compiler is able to parallelize the loop.

The _Restrict keyword is a type qualifier, like volatile, and it qualifies pointer types only. _Restrict is recognized as a keyword only for compilation modes -Xa (default) and -Xt. For these two modes, the compiler defines the macro __RESTRICT to enable users write portable code with restricted pointers.

The compiler defines the macro __RESTRICT to enable users to write portable code with restricted pointers. For example, the following code works on the Sun ANSI/ISO C compiler in all compilation modes, and should work on other compilers which do not support restricted pointers:

#ifdef __RESTRICT

#define restrict _Restrict

#else

#define restrict

#endif

 

void vsq(int n, double * restrict a, double * restrict b)

 

{

 

	 int i;

 

	 for (i=0; i<n; i++) b[i] = a[i] * a[i];

 

}


  















   If restricted pointers become a part of the ANSI/ISO C Standard, it is likely that restrict will be the keyword. Users may want to write code with restricted pointers using:



  
  

    
 

#define restrict _Restrict


  















   as in vsq() because this way there will be minimal changes should restrict become a keyword in the ANSI/ISO C Standard. The Sun ANSI/ISO C compiler uses  _Restrict as the keyword because it is in the implementor's name space, so there is no conflict with identifiers in the user's name space.






   There are situations where a user may not want to change the source code. One can specify pointer-valued function parameters to be treated as restricted pointers with the command-line option -xrestrict; refer to -xrestrict=f for details.






   If a function list is specified, pointer parameters in the specified functions are treated as restricted; otherwise, all pointer parameters in the entire C file are treated as restricted. For example, -xrestrict=vsq would qualify the pointers a and b given in the example with the keyword _Restrict.






   It is critical that _Restrict be used correctly. If pointers qualified as restricted pointers point to objects which are not distinct, loops may be incorrectly parallelized, resulting in undefined behavior. For example, assume that pointers a and b of function vsq() point to objects which overlap, such that b[i] and a[i+1] are the same object. If a and b are not declared as restricted pointers, the loops will be executed serially. If a and b are incorrectly qualified as restricted pointers, the compiler may parallelize the execution of the loops; this is not safe, because b[i+1] should only be computed after b[i] has been computed.






   long long Data Type






   The Sun ANSI/ISO C compiler includes the data types long long, and unsigned long long, which are similar to the data type long. long long can store 64 bits of information; long can store 32 bits of information. long long is not available in -Xc mode.






   Printing long long Data Types 






   To print or scan long long data types, prefix the conversion specifier with the letters "ll." For example, to print llvar, a variable of long long data type, in signed decimal format, use:



  
  

     

printf("%lld\n", llvar);


  














   Usual Arithmetic Conversions 






   Some binary operators convert the types of their operands to yield a common type, which is also the type of the result. These are called the usual arithmetic conversions:






   Constants






   This section contains information related to constants that is specific to the Sun ANSI/ISO C compiler.






   Integral Constants 






   Decimal, octal, and hexadecimal integral constants can be suffixed to indicate type, as shown in the following table.



    

   TABLE 3-1 	  Data Type Suffixes
  
 Suffix
     Type
  

  

    
 u or U
    
 unsigned 
  

  

    
 l or L
    
 long
  

  

    
 ll or LL
    
 long long1
  

  

    
 lu,  LU,  Lu, lU, ul, uL, Ul, or UL
    
 unsigned long
  

  

    
 llu, LLU, LLu, llU, ull, ULL, uLL, Ull
    
 unsigned long long1
  






  

    1
 The long long and unsigned long long are not available in -Xc mode.



  














   When assigning types to unsuffixed constants, the compiler uses the first of this list in which the value can be represented, depending on the size of the constant:






   Character Constants






   A multiple-character constant that is not an escape sequence has a value derived from the numeric values of each character. For example, the constant '123' has a value of: 



  
  

    
 0
    
 '3'
    
 '2'
    
 '1'
  















   or 0x333231.






   With the -Xs option and in other, non-ANSI/ISO versions of C, the value is:



  
  

    
 0
    
 '1'
    
 '2'
    
 '3' 
  















   or 0x313233.






   Include Files






   To include any of the standard header files supplied with the C compilation system, use this format: 



  
  

    
 

#include <stdio.h> 


  















   The angle brackets (<>) cause the preprocessor to search for the header file in the standard place for header files on your system, usually the /usr/include directory.






   The format is different for header files that you have stored in your own directories: 



  
  

    
 

#include "header.h"


  















   The quotation marks (" ") cause the preprocessor to search for header.h first in the directory of the file containing the #include line.






   If your header file is not in the same directory as the source files that include it, specify the path of the directory in which it is stored with the -I option to cc. Suppose, for instance, that you have included both stdio.h and header.h in the source file mycode.c: 



  
  

    
 

#include <stdio.h>

 

#include "header.h"


  















   Suppose further that header.h is stored in the directory../defs. The command:



  
  

    
 

% cc -I../defs mycode.c


  















   directs the preprocessor to search for header.h first in the directory containing mycode.c, then in the directory ../defs, and finally in the standard place. It also directs the preprocessor to search for stdio.h first in ../defs, then in the standard place. The difference is that the current directory is searched only for header files whose names you have enclosed in quotation marks.






   You can specify the -I option more than once on the cc command-line. The preprocessor searches the specified directories in the order they appear. You can specify multiple options to cc on the same command-line:     



  
  

    
 

% cc -o prog -I../defs mycode.c


  















   Nonstandard Floating Point






   IEEE 754 floating-point default arithmetic is "nonstop."  Underflows are "gradual."  The following is a summary, see the Numerical Computation Guide  for details.






   Nonstop means that execution does not halt on occurrences like division by zero, floating-point overflow, or invalid operation exceptions. For example, consider the following, where x is zero and y is positive:






   z = y / x;






   By default, z is set to the value +Inf, and execution continues. With the -fnonstd option, however, this code causes an exit, such as a core dump.






   Here is how gradual underflow works. Suppose you have the following code:



  
  

    
 

x = 10;

 

for (i = 0; i < LARGE_NUMBER; i++)

 

x = x / 10;


  















   The first time through the loop, x is set to 1; the second time through, to 0.1; the third time through, to 0.01; and so on. Eventually, x reaches the lower limit of the machine's capacity to represent its value. What happens the next time the loop runs?






   Let's say that the smallest number characterizable is 1.234567e-38






   The next time the loop runs, the number is modified by "stealing" from the mantissa and "giving" to the exponent so the new value is 1.23456e-39 and, subsequently, 1.2345e-40 and so on. This is known as "gradual underflow," which is the default behavior. In nonstandard mode, none of this "stealing" takes place; typically, x is simply set to zero.






   Preprocessing Directives and Names






   This section describes assertions, pragmas, and predefined names.






   Assertions






   A line of the form: 



  
  

    
 

#assert predicate (token-sequence) 


  















   associates the token-sequence with the predicate in the assertion name space (separate from the space used for macro definitions). The predicate must be an identifier token. 



  
  

    
 

#assert predicate 


  















   asserts that predicate exists, but does not associate any token sequence with it. 






   The compiler provides the following predefined predicates by default (not in -Xc mode):



  
  

    
 

#assert system (unix)

 

#assert machine (sparc)(SPARC)

 

#assert machine (i386)(Intel)

 

#assert cpu (sparc)(SPARC)

 

#assert cpu (i386)(Intel)


  















   lint provides the following predefinition predicate by default (not in -Xc mode):



  
  

    
 

#assert lint (on)


  















   Any assertion may be removed by using #unassert, which uses the same syntax as assert. Using #unassert with no argument deletes all assertions on the predicate; specifying an assertion deletes only that assertion.






   An assertion may be tested in a #if statement with the following syntax: 



  
  

    
 

#if #predicate(non-empty token-list) 


  















   For example, the predefined predicate system can be tested with the following line: 



  
  

    
 

#if #system(unix) 


  















   which evaluates true.






   Pragmas 






   Preprocessing lines of the form: 



  
  

    
 

#pragma pp-tokens 


  















   specify implementation-defined actions.






   The following #pragmas are recognized by the compilation system. The compiler ignores unrecognized pragmas. Using the -v option will give a warning on unrecognized pragmas.






   #pragma align integer (variable[, variable])






   The align pragma makes all the mentioned variables memory aligned to integer bytes, overriding the default. The following limitations apply:






   #pragma does_not_read_global_data (funcname [, funcname])






   This pragma asserts that the specified list of routines do not read global data directly or indirectly. This allows for better optimization of code around calls to such routines. In particular, assignment statements or stores could be moved around such calls.






   This pragma is permitted only after the prototype for the specified functions are declared. If the assertion about global access is not true, then the behavior of the program is undefined. 






   #pragma does_not_return (funcname [, funcname])






   This pragma is an assertion to the compiler backend that the calls to the specified routines will not return. This allows the optimizer to perform optimizations consistent with that assumption. For example, register life-times will terminate at the call sites which in turn allows more optimizations. 






   If the specified function does return, then the behavior of the program is undefined.






   This pragma is permitted only after the prototype for the specified functions are declared as the following example shows:



  
  

    
 

extern void exit(int);

 

#pragma does_note_return(exit);

 

 

extern void __assert(int);

 

#pragma does_not_return(__assert);


  















   #pragma does_not_write_global_data (funcname [, funcname])






   This pragma asserts that the specified list of routines do not write global data directly or indirectly. This allows for better optimization of code around calls to such routines. In particular, assignment statements or stores could be moved around such calls.






   This pragma is permitted only after the prototype for the specified functions are declared. If the assertion about global access is not true, then the behavior of the program is undefined. 






   #pragma error_messages (on|off|default,tag... tag)






   The error message pragma provides control within the source program over the messages issued by the C compiler and lint. For the C compiler, the pragma has an effect on warning messages only. The -w option of the C compiler overrides this pragma by suppressing all warning messages.






   #pragma fini (f1[, f2...,fn])






   Causes the implementation to call functions f1 to fn (finalization functions) after it calls main() routine. Such functions are expected to be of type void and to accept no arguments, and are 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 editors.






   #pragma ident string






   Places string in the .comment section of the executable.






   #pragma init (f1[, f2...,fn])






   Causes the implementation to call functions f1 to fn (initialization functions) before it calls main(). Such functions are expected to be of type void and to accept no arguments, and are called while constructing the memory image of the program at the start of execution. In the case of initializers in a shared object, they are executed during the operation that brings the shared object into memory, either program start-up or some dynamic loading operation, such as dlopen(). The only ordering of calls to initialization functions is the order in which they were processed by the link editors, both static and dynamic.






   #pragma [no_]inline (funcname[, funcname])






   This pragma controls the inlining of routine names listed in the argument of the pragma. The scope of this pragma is over the entire file. Only global inlining control is allowed, call-site specific control is not permitted by this pragma.






   If you use #pragma inline, it provides a suggestion to the compiler to inline the calls in the current file that match the list of routines listed in the pragma. This suggestion may be ignored under certain cases. For example, the suggestion is ignored when the body of the function is in a different module and the crossfile option is not used.






   If you use #pragma no_inline, it provides a suggestion to the compiler to not inline the calls in the current file that match the list of routines listed in the pragma.






   Both #pragma inline and #pragma no_inline are permitted only after the prototype for the specified functions are declared as the following example shows:



  
  

    
 

static void foo(int);

 

static int bar(int, char *);

 

#pragma inline(foo, bar) 


  















   #pragma int_to_unsigned (funcname)






   For a function that returns a type of unsigned, in -Xt or -Xs mode, changes the function return to be of type int.






   (SPARC) #pragma MP serial_loop






   Refer to Serial Pragmas for details.






   (SPARC) #pragma MP serial_loop_nested






   Refer to Serial Pragmas for details.






   (SPARC) #pragma MP taskloop






   Refer to Parallel Pragma for details.






   (SPARC) #pragma nomemorydepend






   This pragma specifies that for any iteration of a loop, there are no memory dependences. That is, within any iteration of a loop there are no references to the same memory. This pragma will permit the compiler (pipeliner) to schedule instructions, more effectively, within a single iteration of a loop. If any memory dependences exist within any iteration of a loop, the results of executing the program are undefined. The pragma applies to the next for loop within the current block. The compiler takes advantage of this information at optimization level of 3 or above. 






   (SPARC) #pragma no_side_effect(funcname[, funcname]) 






   funcname specifies the name of a function within the current translation unit. The function must be declared prior to the pragma. The pragma must be specified prior to the function's definition. For the named function, funcname, the pragma declares that the function has no side effects of any kind. This means that funcname returns a result value that depends only on the passed arguments.  In addition, funcname and any called descendants:






   The compiler can use this information when doing optimizations using the function. If the function does have side effects, the results of executing a program which calls this function are undefined. The compiler takes advantage of this information at optimization level of 3 or above.






   #pragma opt level (funcname[, funcname])






   The value of level specifies the optimization level for the funcname subprograms. You can assign opt levels zero, one, two three, four, and five. You can turn off optimization by setting level to 0. The funcname subprograms must be prototyped prior to the pragma. 






   The level of optimization for any function listed in the pragma is reduced to the value of -xmaxopt. The pragma is ignored when -xmaxopt=off.






   #pragma pack(n)






   Use #pragma pack(n), to affect member packing of a structure. By default, members of a structure are aligned on their natural boundaries; one byte for a char, two bytes for a short, four bytes for an integer etc. If n is present, it must be a power of 2 specifying the strictest natural alignment for any structure member. Zero is not accepted.






   You can use #pragma pack(n) to specify an alignment boundary for a structure member. For example, #pragma pack(2) aligns int, long, long long, float, double, long double, and pointers on two byte boundaries instead of their natural alignment boundaries. 






   If n is the same or greater than the strictest alignment on your platform, (four on Intel, eight on SPARC v8, and 16 on SPARC v9), the directive has the effect of natural alignment. Also, if n is omitted, member alignment reverts to the natural alignment boundaries.






   The #pragma pack(n) 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 #pragma pack(n) prior to including a header that defines the interface of a precompiled library. The recommended usage of #pragma pack(n) is to place it in your program code immediately before any structure to be packed. Follow the packed structure immediately with #pragma pack().






   Note – If you use #pragma pack to align struct members on boundaries other than their natural boundaries, accessing these fields may lead to a bus error on SPARC. See -xmemalign=ab, for the optimal way to compile such programs. 






   (SPARC) #pragma pipeloop(n)






   This pragma accepts a positive constant integer value, or 0, for the argument n. This pragma specifies that a loop is pipelinable and the minimum dependence distance of the loop-carried dependence is n. If the distance is 0, then the loop is effectively a Fortran-style doall loop and should be pipelined on the target processors.   If the distance is greater than 0, then the compiler (pipeliner) will only try to pipeline n successive iterations. The pragma applies to the next for loop within the current block. The compiler takes advantage of this information at optimization level of 3 or above.






   #pragma rarely_called(funcname[, funcname])






   This pragma provides a hint to the compiler backend that the specified functions are called infrequently. This allows the compiler to perform profile-feedback style optimizations on the call-sites of such routines without the overhead of a profile-collections phase. Since this pragma is a suggestion, the compiler optimizer may not perform any optimizations based on this pragma.






   The #pragma rarely_called preprocessor directive is only permitted after the prototype for the specified functions are declares. The following is an example of #pragma rarely_called:



  
  

    
 

extern void error (char *message);

 

#pragma rarely_called(error);


  















   #pragma redefine_extname old_extname new_extname






   This pragma causes every externally defined occurrence of the name old_extname in the object code to be replaced by new_extname. As a result, the linker only sees the name new_extname at link time. If #pragma redefine_extname is encountered after the first use of old_extname, as a function definition, an initializer, or an expression, the effect is undefined. (This pragma is not supported in -Xs mode.)






   When #pragma redefine_extname is available, the compiler provides a definition of the predefined macro PRAGMA_REDEFINE_EXTNAME which lets you write portable code that works both with and without #pragma redefine_extname.






   The purpose of #pragma redefine_extname is to allow an efficient means of redefining a function interface when the name of the function cannot be changed. For example, when the original function definition must be maintained in a library, for compatibility with existing programs, along with a new definition of the same function for use by new programs. This can be accomplished by adding the new function definition to the library by a new name. Consequently, the header file that declares the function uses #pragma redefine_extname so that all of the uses of the function are linked with the new definition of that function.



  
  

    
 

#if    defined(__STDC__)

 

 

#ifdef __PRAGMA_REDEFINE_EXTNAME

 

extern int myroutine(const long *, int *);

 

#pragma redefine_extname myroutine __fixed_myroutine

 

#else /* __PRAGMA_REDEFINE_EXTNAME */

 

 

static int

 

myroutine(const long * arg1, int * arg2)

 

{

 

    extern int __myroutine(const long *, int*);

 

    return (__myroutine(arg1, arg2));

 

}

 

#endif /* __PRAGMA_REDEFINE_EXTNAME */

 

 

#else /* __STDC__ */

 

 

#ifdef __PRAGMA_REDEFINE_EXTNAME

 

extern int myroutine();

 

#pragma redefine_extnmae myroutine __fixed_myroutine

 

#else /* __PRAGMA_REDEFINE_EXTNAME */

 

 

static int

 

myroutine(arg1, arg2)

 

    long *arg1;

 

    int *arg2;

 

{

 

    extern int __fixed_myroutine();

 

    return (__fixed_myroutine(arg1, arg2));

 

}

 

#endif /* __PRAGMA_REDEFINE_EXTNAME */

 

 

#endif /* __STDC__ */


  















   #pragma returns_new_memory (funcname[, funcname])






   This pragma asserts that the return value of the specified functions does not alias with any memory at the call site. In effect, this call returns a new memory location. This informations allows the optimizer to better track pointer values and clarify memory location. This results in improved scheduling, pipelining, and parallelization of loops. However, if the assertion is false, the behavior of the program is undefined.






   This pragma is permitted only after the prototype for the specified functions are declared as the following example shows:



  
  

    
 

void *malloc(unsigned);

 

#pragma returns_new_memory(malloc);


  















   #pragma unknown_control_flow (name[, name])






   In order to describe procedures that alter the flow graphs of their callers, the C compiler provides the #pragma unknown_control_flow directive. Typically, this directive accompanies declarations of functions like setjmp(). On Sun systems, the include file <setjmp.h> contains the following:



  
  

    
 

extern int setjmp();

 

#pragma unkown_control_flow(setjmp);


  















   Other functions with properties like those of setjmp() must be declared similarly.






   In principle, an optimizer that recognizes this attribute could insert the appropriate edges in the control flow graph, thus handling function calls safely in functions that call setjmp(), while maintaining the ability to optimize code in unaffected parts of the flow graph.






   (SPARC) #pragma unroll (unroll_factor)






   This pragma accepts a positive constant integer value for the argument unroll_factor. The pragma applies to the next for loop within the current block. For unroll factor other than 1, this directive serves as a suggestion to the compiler that the specified loop should be unrolled by the given factor. The compiler will, when possible, use that unroll factor. When the unroll factor value is 1, this directive serves as a command which specifies to the compiler that the loop is not to be unrolled. The compiler takes advantage of this information at optimization level of 3 or above.






   #pragma weak symbol1 [= symbol2]






   Defines a weak global symbol. This pragma is used mainly in source files for building libraries. The linker does not produce an error message if it is unable to resolve a weak symbol.



  
  

    
 

#pragma weak symbol


  















   defines symbol to be a weak symbol. The linker does not produce an error message if it does not find a definition for symbol.



  
  

    
 

#pragma weak symbol1 = symbol2


  















   defines symbol1 to be a weak symbol, which is an alias for the symbol symbol2. This form of the pragma can only be used in the same translation unit where symbol2 is defined, either in the sourcefiles or one of its included headerfiles. Otherwise, a compilation error will result.






   If your program calls but does not define symbol1, and symbol1 is a weak symbol in a library being linked, the linker uses the definition from that library. However, if your program defines its own version of symbol1, then the program's definition is used and the weak global definition of symbol1 in the library is not used. If the program directly calls symbol2, the definition from the library is used; a duplicate definition of symbol2 causes an error.






   Variable Argument Lists for #define






   The C compiler accepts #define preprocessor directives of the following form:



  
  

    
 

#define identifier (...) replacement_list

 

#define identifier (identifier_list, ...) replacement_list


  















   If the identifier_list in the macro definition ends with an ellipses, it means that there will be more arguments in the invocation than there are parameters in the macro definition, excluding the ellipsis. Otherwise, the number of parameters in the macro definition, including those arguments which consist of no preprocessing tokens, matches the number of arguments. Use the identifier __VA_ARGS__ in the replacement list of a #define preprocessing directive which uses the ellipsis notation in its arguments. The following example demonstrates the variable argument list macro facilities.



  
  

    
 

#define debug(...) fprintf(stderr, __VA_ARGS__)

 

#define showlist(...) puts(#__VA_ARGS__)

 

#define report(test, ...) ((test)?puts(#test):\

 

	 	 	 	 	 	 printf(__VA_ARGS__))

 

debug("Flag");

 

debug("X = %d\n",x);

 

showlist(The first, second, and third items.);

 

report(x>y, "x is %d but y is %d", x, y);


  















   which results in the following:



  
  

    
 

fprintf(stderr, "Flag");

 

fprintf(stderr, "X = %d\n", x);

 

puts("The first, second, and third items.");

 

((x>y)?puts("x>y"):printf("x is %d but y is %d", x, y));


  















   Predefined Data






   The compiler predefines a static, constant, char array named __func__ for every function definition. The array is initialized with the name of the function and can be used anywhere a static function scope array may be used. For example, use the array to print the name of the enclosing function.



  
  

    
 

#include <stdio.h>

 

void the_func(void) 

 

{

 

     printf("%s\n", __func__);

 

     /* ... */

 

}


  















   Each time the function is  called, it prints the_func to the standard output.






   Predefined Names 






   The following identifier is predefined as an object-like macro: 



   TABLE 3-2 	  Predefined Identifier
  

    
 Identifier
    
 Description
  

  

    
 __STDC__ 
    
 __STDC__ 1 -Xc __STDC__ 0 -Xa, -Xt Not defined  -Xs
  















   The compiler issues a warning if __STDC__ is undefined (#undef __STDC__). __STDC__ is not defined in -Xs mode.    






   Predefinitions (not valid in -Xc mode):






   The following predefinitions are valid in all modes:






   The compiler also predefines the object-like macro __PRAGMA_REDEFINE_EXTNAME to indicate that the pragma will be recognized. The following is predefined in -Xa and -Xt modes only:






   __RESTRICT

















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