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Synopsis:
    #include <stdarg.h>
    #include <stdio.h>
    int vfprintf( FILE *fp,
                  const char *format,
                  va_list arg );
    #include <stdarg.h>
    #include <stdio.h>
    #include <wchar.h>
    int vfwprintf( FILE *fp,
                   const wchar_t *format,
                   va_list arg );

Description:
    The vfprintf function writes output to the file pointed to by fp under
    control of the argument format.  The format string is described under
    the description of the  printf function.  The vfprintf function is
    equivalent to the  fprintf function, with the variable argument list
    replaced with arg, which has been initialized by the  va_start macro.

    The vfwprintf function is identical to vfprintf except that it accepts a
    wide-character string argument for format.

Returns:
    The vfprintf function returns the number of characters written, or a
    negative value if an output error occurred.  The vfwprintf function
    returns the number of wide characters written, or a negative value if an
    output error occurred.  When an error has occurred,  errno contains a
    value indicating the type of error that has been detected.

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

    FILE *LogFile;

    /* a general error routine */

    void errmsg( char *format, ... )
      {
        va_list arglist;

        fprintf( stderr, "Error: " );
        va_start( arglist, format );
        vfprintf( stderr, format, arglist );
        va_end( arglist );
        if( LogFile != NULL ) {
          fprintf( LogFile, "Error: " );
          va_start( arglist, format );
          vfprintf( LogFile, format, arglist );
          va_end( arglist );
        }
      }

    void main()
      {
        LogFile = fopen( "error.log", "w" );
        errmsg( "%s %d %s", "Failed", 100, "times" );
      }

Classification:
    vfprintf is ANSI, vfwprintf is ANSI

Systems:
     vfprintf - All, Netware

    vfwprintf - All

See Also:
    _bprintf, cprintf, fprintf, printf, sprintf, va_arg, va_end, va_start,
    _vbprintf, vcprintf, vprintf, vsprintf