Syntax

#include <stdarg.h>
var_type va_arg(va_list arg_ptr, var_type);
void va_end(va_list arg_ptr);
void va_start(va_list arg_ptr, variable_name);

va_arg, va_end, and va_start access the arguments to a function when it takes a fixed number of required arguments and a variable number of optional arguments. All three of these are macros. You declare required arguments as ordinary parameters to the function and access the arguments through the parameter names.

va_start initializes the arg_ptr pointer for subsequent calls to va_arg and va_end.

The argument variable_name is the identifier of the rightmost named parameter in the parameter list (preceding , ...). Use va_start before va_arg. Corresponding va_start and va_end macros must be in the same function.

va_arg retrieves a value of the given var_type from the location given by arg_ptr, and increases arg_ptr to point to the next argument in the list. va_arg can retrieve arguments from the list any number of times within the function. The var_type argument must be one of int, long, double, struct, union, or pointer, or a typedef of one of these types.

va_end is needed to indicate the end of parameter scanning.

va_arg returns the current argument. va_end and va_start do not return a value.

This example passes a variable number of arguments to a function, stores each argument in an array, and prints each argument.

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

int vout(int max,...);

int main(void)
{
   vout(3, "Sat", "Sun", "Mon");
   printf("\n");
   vout(5, "Mon", "Tues", "Wed", "Thurs", "Fri");
   return 0;
}

int vout(int max,...)
{
   va_list arg_ptr;
   int args = 0;
   char *days[7];

   va_start(arg_ptr, max);
   while (args < max) {
      days[args] = va_arg(arg_ptr, char *);
      printf("Day:  %s  \n", days[args++]);
   }
   va_end(arg_ptr);

   /****************************************************************************
      The output should be:

      Day:  Sat
      Day:  Sun
      Day:  Mon

      Day:  Mon
      Day:  Tues
      Day:  Wed
      Day:  Thurs
      Day:  Fri
   ****************************************************************************/
}

• vfprintf
  
• vprintf
  
• vsprintf

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