Before ISO 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 ISO C facility, since support
for ISO 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 only 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.
Published under the terms of the GNU General Public License
