vfprintf_s, _vfprintf_s_l, vfwprintf_s, _vfwprintf_s_l

Article
06/05/2017

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The latest version of this topic can be found at vfprintf_s, _vfprintf_s_l, vfwprintf_s, _vfwprintf_s_l.

Write formatted output using a pointer to a list of arguments. These are versions of vfprintf, _vfprintf_l, vfwprintf, _vfwprintf_l with security enhancements as described in Security Features in the CRT.

Syntax

int vfprintf_s(  
   FILE *stream,  
   const char *format,  
   va_list argptr   
);  
int _vfprintf_s_l(  
   FILE *stream,  
   const char *format,  
   locale_t locale,  
   va_list argptr   
);  
int vfwprintf_s(  
   FILE *stream,  
   const wchar_t *format,  
   va_list argptr   
);  
int _vfwprintf_s_l(  
   FILE *stream,  
   const wchar_t *format,  
   locale_t locale,  
   va_list argptr   
);

Parameters

stream
Pointer to FILE structure.

format
Format specification.

argptr
Pointer to list of arguments.

locale
The locale to use.

For more information, see Format Specifications.

Return Value

vfprintf_s and vfwprintf_s return the number of characters written, not including the terminating null character, or a negative value if an output error occurs. If either stream or format is a null pointer, or if the format string contains invalid formatting characters, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, the functions return -1 and set errno to EINVAL.

For information on these and other error codes, see _doserrno, errno, _sys_errlist, and _sys_nerr.

Remarks

Each of these functions takes a pointer to an argument list, then formats and writes the given data to stream.

These functions differ from the non-secure versions only in that the secure versions check that the format string contains valid formatting characters.

vfwprintf_s is the wide-character version of vfprintf_s; the two functions behave identically if the stream is opened in ANSI mode. vfprintf_s doesn't 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.

Important

Ensure that format is not a user-defined string. For more information, see Avoiding Buffer Overruns.

Generic-Text Routine Mappings

TCHAR.H routine	_UNICODE & _MBCS not defined	_MBCS defined	_UNICODE defined
`_vftprintf_s`	`vfprintf_s`	`vfprintf_s`	`vfwprintf_s`
`_vftprintf_s_l`	`_vfprintf_s_l`	`_vfprintf_s_l`	`_vfwprintf_s_l`

Requirements

Routine	Required header	Optional headers
`vfprintf_s`, _`vfprintf_s_l`	<stdio.h> and <stdarg.h>	<varargs.h>*
`vfwprintf_s`, _`vfwprintf_s_l`	<stdio.h> or <wchar.h>, and <stdarg.h>	<varargs.h>*

* Required for UNIX V compatibility.

For additional compatibility information, see Compatibility in the Introduction.

.NET Framework Equivalent

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.

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