C Standard Library Reference Guide (stdarg.h)

Stdarg.h

The Stdarg header file defines a macro that is used to get arguments when the function argument is in the number position.

Macro:

Va_start ();

Va_arg ();

Va_end ();

Type:

typedef va_list

10.1. Variables and definitions

Va_list applies to the type of parameters that enter a function with Stdarg macros.

A function with an indeterminate number of parameters, used (,...) Marked at the end of the argument list.

10.2. Va_start

Statement:

void Va_start (Va_list ap, Last_arg);

Initializes an AP that is used in conjunction with the VA_ARG and Va_end macros. Last_arg is the most-determined parameter (which argument precedes the ellipsis) that is passed to the function. Note that Va_start is invoked before using Va_arg and Va_end.

10.3. Va_arg

Statement:

Type Va_arg (va_list ap, type);

A situation that follows another parameter type after the argument list (that is, the AP). Note that the AP must be initialized by Va_start. If there is no next argument, the result is undefined.

10.4. Va_end

Statement:

void Va_end (va_list ap);

Allows a function with a parameter to call the macro va_start to return. If Va_end is not called before the function returns, the result is undefined. The argument list AP is not allowed to be used until Va_end is invoked and Va_start is not invoked.

Instance:

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

void sum (char *, int, ...);   


int main (void)   
       
{   

  sum ("The sum of 10+15+13 is%d.\n", 3,10,15,13);   

  return 0;   

}   


void sum (char *string, int num_args, ...)   

{   

  int sum=0;   

  Va_list ap;   

  int loop;   


  Va_start (Ap,num_args);   

  for (loop=0;loop<num_args;loop++)   

    sum+=va_arg (ap,int);   


  printf (string,sum); 

  Va_end (AP);   

}

Original English: http://www.acm.uiuc.edu/webmonkeys/book/c_guide/2.10.html

Original Author: Eric Huss

Chinese translator: Liu Yong poechant

Copyright: The original copy of this article is owned by Eric Huss, and the Chinese translation is poechant All rights reserved. Reprint please specify from "Liuda csdn blog": http://blog.csdn.net/poechant