< c‎ | variadic
Defined in header <stdarg.h>
void va_start( va_list ap, parmN );

The va_start macro enables access to the variable arguments following the named argument parmN.

va_start should be invoked with an instance to a valid va_list object ap before any calls to va_arg.

If parmN is declared with register storage class specifier, with an array type, with a function type, or with a type not compatible with the type that results from default argument promotions, the behavior is undefined.


[edit] Parameters

ap - an instance of the va_list type
parmN - the named parameter preceding the first variable parameter

[edit] Expanded value


[edit] Example

#include <stdio.h>
#include <stdarg.h>
int add_nums(int count, ...) 
    int result = 0;
    va_list args;
    va_start(args, count);
    for (int i = 0; i < count; ++i) {
        result += va_arg(args, int);
    return result;
int main(void) 
    printf("%d\n", add_nums(4, 25, 25, 50, 50));

Possible output:


[edit] References

  • C11 standard (ISO/IEC 9899:2011):
  • The va_start macro (p: 271-272)
  • C99 standard (ISO/IEC 9899:1999):
  • The va_start macro (p: 251-252)
  • C89/C90 standard (ISO/IEC 9899:1990):
  • The va_start macro

[edit] See also

accesses the next variadic function argument
(function macro) [edit]
makes a copy of the variadic function arguments
(function macro) [edit]
ends traversal of the variadic function arguments
(function macro) [edit]
holds the information needed by va_start, va_arg, va_end, and va_copy
(typedef) [edit]
C++ documentation for va_start