C library macro - va_start ()

C standard library - <stdarg.h>

description

C library macrovoid va_start (va_list ap, last_arg) apinitialized variable, itva_argandva_endmacros are used together.last_arg passed to the function is the last known fixed parameter, the ellipsis previous parameters.

This macro must be called before usingva_arg and va_end.

statement

Here is the va_start () macro statement.

void va_start(va_list ap, last_arg);

parameter

• ap - it is an object of type va_listwhich is used to store additional parameters through theva_argget the necessary information.
• last_arg - last function known fixed parameter passed to it.

return value

NA

Examples

The following example demonstrates the va_start () macro usage.

#include<stdarg.h>
#include<stdio.h>

int sum(int, ...);

int main(void)
{
   printf("10、20 和 30 的和 = %d\n",  sum(3, 10, 20, 30) );
   printf("4、20、25 和 30 的和 = %d\n",  sum(4, 4, 20, 25, 30) );

   return 0;
}

int sum(int num_args, ...)
{
   int val = 0;
   va_list ap;
   int i;

   va_start(ap, num_args);
   for(i = 0; i < num_args; i++)
   {
      val += va_arg(ap, int);
   }
   va_end(ap);
 
   return val;
}

Let's compile and run the above program, which will result in the following:

10、20 和 30 的和 = 60
4、20、25 和 30 的和 = 79

C standard library - <stdarg.h>