NAME

vprintf, vfprintf, vsprintf − print formatted output of a variable argument list

SYNOPSIS

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

int vprintf(const char ∗format, va_list ap);

int vfprintf(FILE ∗stream, const char ∗format, va_list ap);

int vsprintf(char ∗s, const char ∗format, va_list ap);

MT-LEVEL

See the NOTES section of this page. 

DESCRIPTION

vprintf(), vfprintf(), and vsprintf() are the same as printf(), fprintf(), and sprintf() respectively, except that instead of being called with a variable number of arguments, they are called with an argument list as defined by the <stdarg.h> header. 

The <stdarg.h> header defines the type va_list and a set of macros for advancing through a list of arguments whose number and types may vary.  The argument ap to the vprint family of routines is of type va_list.  This argument is used with the <stdarg.h> header file macros va_start(), va_arg(), and va_end() (see stdarg(5)).  The EXAMPLES section below shows the use of va_start() and va_end() with vprintf(). 

The macro va_alist is used as the parameter list in a function definition, as in the function called error() in the example below.  The macro va_start(ap, parmN), where ap is of type va_list, and parmN is the rightmost parameter (just before ...), must be called before any attempt to traverse and access unnamed arguments is made. The va_end(ap) macro must be invoked when all desired arguments have been accessed.  (The argument list in ap can be traversed again if va_start() is called again after va_end().)  In the example below, the error() arguments, arg1, arg2, ..., are given to vfprintf() in the argument ap.

RETURN VALUES

vprintf() and vfprintf() return the number of characters transmitted, or return −1 if an error was encountered. 

EXAMPLES

The following demonstrates how vfprintf() could be used to write an error routine:

#include <stdio.h>
#include <stdarg.h>
. . .
/∗
 ∗   error should be called like
 ∗         error(function_name, format, arg1, ...);
 ∗/
void error(char ∗function_name, char ∗format, ...)
{
    va_list ap;
    va_start(ap, );
    /∗ print out name of function causing error ∗/
    (void) fprintf(stderr, "ERR in %s: ", function_name);
    /∗ print out remainder of message ∗/
    (void) vfprintf(stderr, format, ap);
    va_end(ap);
    (void) abort;
}

SEE ALSO

printf(3S), stdarg(5)

NOTES

vprintf(), vfprintf(), and vsprintf() are MT-Safe in multi-thread applications. 

SunOS 5.5/SPARC  —  Last change: 13 Apr 1994