fprintf, _fprintf_l, fwprintf, _fwprintf_l

Article
04/22/2008

Print formatted data to a stream. More secure versions of these functions are available; see fprintf_s, _fprintf_s_l, fwprintf_s, _fwprintf_s_l.

int fprintf( 
   FILE *stream,
   const char *format [,
      argument ]...
);
int _fprintf_l( 
   FILE *stream,
   const char *format,
   locale_t locale [,
      argument ]...
);
int fwprintf( 
   FILE *stream,
   const wchar_t *format [,
      argument ]...
);
int _fwprintf_l( 
   FILE *stream,
   const wchar_t *format,
   locale_t locale [,
      argument ]...
);

Parameters

stream
Pointer to FILE structure.
format
Format-control string.
argument
Optional arguments.
locale
The locale to use.

Return Value

fprintf returns the number of bytes written. fwprintf returns the number of wide characters written. Each of these functions returns a negative value instead when an output error occurs. If stream or format is NULL, these functions invoke the invalid parameter handler, as described in Parameter Validation. If execution is allowed to continue, the functions return -1 and set errno to EINVAL. The format string is not checked for valid formatting characters as it is when using fprintf_s or fwprintf_s.

See _doserrno, errno, _sys_errlist, and _sys_nerr for more information on these, and other, error codes.

Remarks

fprintf formats and prints a series of characters and values to the output stream*.* Each function argument (if any) is converted and output according to the corresponding format specification in format*.* For fprintf, the format argument has the same syntax and use that it has in printf.

fwprintf is a wide-character version of fprintf; in fwprintf, format is a wide-character string. These functions behave identically if the stream is opened in ANSI mode. fprintf does not currently support output into a UNICODE stream.

The versions of these functions with the _l suffix are identical except that they use the locale parameter passed in instead of the current thread locale.

Security Note:
Ensure that format is not a user-defined string.

Generic-Text Routine Mappings

TCHAR.H routine	_UNICODE & _MBCS not defined	_MBCS defined	_UNICODE defined
_ftprintf	fprintf	fprintf	fwprintf
_ftprintf_l	_fprintf_l	_fprintf_l	_fwprintf_l

For more information, see Format Specifications.

Requirements

Function	Required header
fprintf, _fprintf_l	<stdio.h>
fwprintf, _fwprintf_l	<stdio.h> or <wchar.h>

For additional compatibility information, see Compatibility in the Introduction.

Example

// crt_fprintf.c
/* This program uses fprintf to format various
 * data and print it to the file named FPRINTF.OUT. It
 * then displays FPRINTF.OUT on the screen using the system
 * function to invoke the operating-system TYPE command.
 */

#include <stdio.h>
#include <process.h>

FILE *stream;

int main( void )
{
   int    i = 10;
   double fp = 1.5;
   char   s[] = "this is a string";
   char   c = '\n';

   fopen_s( &stream, "fprintf.out", "w" );
   fprintf( stream, "%s%c", s, c );
   fprintf( stream, "%d\n", i );
   fprintf( stream, "%f\n", fp );
   fclose( stream );
   system( "type fprintf.out" );
}

this is a string
10
1.500000

.NET Framework Equivalent

System::IO::StreamWriter::Write

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