varargs(3)

Name

varargs − variable argument list

Syntax

#include <varargs.h>

function (va_alist)
va_dcl
va_list pvar;
va_start (pvar);
f = va_arg (pvar, type);
va_end (pvar);

Description

This set of macros provides a means of writing portable procedures that accept variable argument lists. Routines having variable argument lists, such as printf(,), that do not use varargs are inherently nonportable, since different machines use different argument passing conventions.

va_alist is used in a function header to declare a variable argument list.

va_dcl is a declaration for va_alist. Note that there is no semicolon after va_dcl.

va_list is a type which can be used for the variable pvar, which is used to traverse the list. One such variable must always be declared.

va_start (pvar) is called to initialize pvar to the beginning of the list.

va_arg (pvar, type) will return the next argument in the list pointed to by pvar. The 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, since it cannot be determined at runtime.

va_end (pvar) is used to finish up.

Multiple traversals, each bracketed by va_start ... va_end, are possible.

Examples

#include <varargs.h>
execl(va_alist)
va_dcl
{
va_list ap;
char *file;
char *args[100];
int argno = 0;
va_start(ap);
file = va_arg(ap, char *);
while (args[argno++] = va_arg(ap, char *))
B;
va_end(ap);
return execv(file, args);
}

Restrictions