va_arg, va_copy, va_start, and va_end : Variable Number of Arguments « Function « C Tutorial

1. C Tutorial
2. Function
3. Variable Number of Arguments

Use va_arg(), va_start(), and va_end() macros together to pass a variable number of arguments to a

function. For example, printf(). The type va_list is defined by .

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

  double sum_series(int num, ...);

  /* Variable length argument example - sum a series. */
  int main(void)
  {
    double d;

    d = sum_series(5, 0.5, 0.25, 0.125, 0.0625, 0.03125);

    printf("Sum of series is %f.\n", d);
    return 0;
  }

  double sum_series(int num, ...)
  {
    double sum=0.0, t;
    va_list argptr;

    /* initialize argptr */
    va_start(argptr, num);

    /* sum the series */
    for( ; num; num--) {
      t = va_arg(argptr, double); /* get next argument */
      sum += t;
    }

    /* do orderly shutdown */
    va_end(argptr);
    return sum;
  }

Sum of series is 0.968750.