fprintf, _fprintf_l, fwprintf, _fwprintf_l

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 ]...


  • 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.


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 noteSecurity 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









For more information, see Format Specifications.



Required header

fprintf, _fprintf_l


fwprintf, _fwprintf_l

<stdio.h> or <wchar.h>

For additional compatibility information, see Compatibility in the Introduction.


// 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

.NET Framework Equivalent


See Also


Stream I/O

_cprintf, _cprintf_l, _cwprintf, _cwprintf_l

fscanf, _fscanf_l, fwscanf, _fwscanf_l

sprintf, _sprintf_l, swprintf, _swprintf_l, __swprintf_l

Format Specification Fields: printf and wprintf Functions