vfprintf - Print Argument Data to Stream

Syntax

#include <stdarg.h>
#include <stdio.h>
int vfprintf(FILE *stream, const char *format, va_list arg_ptr);

vfprintf formats and writes a series of characters and values to the output stream. vfprintf works just like fprintf, except that arg_ptr points to a list of arguments whose number can vary from call to call in the program. These arguments should be initialized by va_start for each call. In contrast, fprintf can have a list of arguments, but the number of arguments in that list is fixed when you compile the program.

vfprintf converts each entry in the argument list according to the corresponding format specifier in format. The format has the same form and function as the format string for printf. For a description of the format string, see printf.

In extended mode, vfprintf also converts floating-point values of NaN and infinity to the strings "NAN" or "nan" and "INFINITY" or "infinity". The case and sign of the string is determined by the format specifiers. See Infinity and NaN Support for more information on infinity and NaN values.

If successful, vfprintf returns the number of bytes written to stream. If an error occurs, the function returns a negative value.

This example prints out a variable number of strings to the file vfprintf.out.

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

#define FILENAME "vfprintf.o"

void vout(FILE *stream, char *fmt,...);

char fmt1[] = "%s  %s  %s  %s\n";

int main(void)
{
   FILE *stream;

   stream = fopen(FILENAME, "w");
   vout(stream, fmt1, "Sat", "Sun", "Mon", "Tue");
   fclose(stream);
   return 0;

   /****************************************************************************
      After running the program, the output file should contain:

      Sat  Sun  Mon  Tue
   ****************************************************************************/
}

void vout(FILE *stream, char *fmt,...)
{
   va_list arg_ptr;

   va_start(arg_ptr, fmt);
   vfprintf(stream, fmt, arg_ptr);
   va_end(arg_ptr);
}

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