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On my system (Mac OS 10.6) /usr/include/stdarg.h is:
/* This file is public domain. */
/* GCC uses its own copy of this header */
#if defined(__GNUC__)
#include_next <stdarg.h>
#elif defined(__MWERKS__)
#include "mw_stdarg.h"
#else
#error "This header only supports __MWERKS__."
#endif
So, if GCC uses its own copy of stdarg.h, where is it? I have no idea on what
that #include_next means (maybe a GCC extension?), nor something about
"MWERKS" (a compiler?).
810
The stdarg. h header file defines macros used to access arguments in functions with variable-length argument lists. The stdarg. h header file also defines the structure va_list .
h header file to extract the values stored in the variable argument list--va_start, which initializes the list, va_arg, which returns the next argument in the list, and va_end, which cleans up the variable argument list.
va_list is a complete object type suitable for holding the information needed by the macros va_start, va_copy, va_arg, and va_end. If a va_list instance is created, passed to another function, and used via va_arg in that function, then any subsequent use in the calling function should be preceded by a call to va_end.
<stdarg.h>, even more than most C library headers, tends to be very compiler-specific. As such, each of the compilers on OS X has it's own stdarg.h implementation, found in a compiler-specific location (which is included as part of the default search paths for that compiler). The compiler finds the generic stdarg.h, which basically tells it to "keep looking" (via the extension #include_next), and it then finds the compiler-specific implementation.
__MWERKS__ refers to an old compiler for PPC, "MetroWerks CodeWarrior".
78
#include_next is a gcc extension. As you should know, #include has a list of paths it searches for header files. #include_next tells the preprocessor to include the specified header checking only paths in the list after the one that contained the current header file.
__MWERKS__ is a preprocessor macro defined on old versions of CodeWarrior.
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