stdarg(5) File Formats Manual stdarg(5)
NAME
stdarg.h - macros for handling variable argument lists
SYNOPSIS
DESCRIPTION
The header contains a set of macros that can be used to write portable procedures that accept variable argument lists. Routines that have
variable argument lists (such as but do not use stdarg are inherently nonportable, because different machines use different argument-pass-
ing conventions.
is a type defined for the variable used to traverse the list.
is called to initialize pvar to the beginning of the list. The type of argN should be the same as the argument to the function just before
the variable portion of the argument list.
returns the next argument in the list pointed to by pvar. type is the type the argument is expected to be. Different types can be mixed,
but it is up to the routine to know what type of argument is expected, because it cannot be determined at runtime.
is used to clean up.
Multiple traversals, each bracketed by ... are possible.
NOTE: The header file supercedes the header, and contains all of the macros. is provided for compatibility with pre-ANSI compilers and
earlier releases of HP C/HP-UX.
EXAMPLE
This example is a possible implementation of (see exec(2)):
#include <stdarg.h>
#define MAXARGS 100
/* execl is called by
execl(file, arg1, arg2, ..., (char *)0);
*/
execl(const char *file, const char *args, ...)
{
va_list ap;
char *array[MAXARGS];
int argno = 0;
va_start(ap, args);
if ((array[0] = args) != 0)
while ((array[argno++] = va_arg(ap, char *)) != 0)
;
va_end(ap);
return execv(file, array);
}
WARNINGS
It is up to the calling routine to specify how many arguments there are, since it is not always possible to determine this from the stack
frame. For example, is passed a zero pointer to signal the end of the list, and can tell how many arguments are there by the format
string.
Unless ANSI C is used, it is non-portable to specify a second argument of char, short, or float to va_arg, because arguments seen by the
called function are never char, short, or float.
Pre-ANSI C converts char and short arguments to int and converts float arguments to double before passing them to a function.
SEE ALSO
exec(2), vprintf(3S), varargs(5).
STANDARDS CONFORMANCE
stdarg(5)
