The GNU C Library - Old Varargs

Old-Style Variadic Functions

Before ANSI C, programmers used a slightly different facility for writing variadic functions. The GNU C compiler still supports it; currently, it is more portable than the ANSI C facility, since support for ANSI C is still not universal. The header file which defines the old-fashioned variadic facility is called `varargs.h'.

Using `varargs.h' is almost the same as using `stdarg.h'. There is no difference in how you call a variadic function; See Calling Variadics. The only difference is in how you define them. First of all, you must use old-style non-prototype syntax, like this:

	tree
	build (va_alist)
	     va_dcl
	{

Secondly, you must give va_start just one argument, like this:

	  va_list p;
	  va_start (p);

These are the special macros used for defining old-style variadic functions:

Macro va_alist

This macro stands for the argument name list required in a variadic function.

Macro va_dcl

This macro declares the implicit argument or arguments for a variadic function.

Macro void va_start (va_list ap)

This macro, as defined in `varargs.h', initializes the argument pointer variable ap to point to the first argument of the current function.

The other argument macros, va_arg and va_end , are the same in `varargs.h' as in `stdarg.h'; see Argument Macros for details.

It does not work to include both `varargs.h' and `stdarg.h' in the same compilation; they define va_start in conflicting ways.