vprintf_s, _vprintf_s_l, vwprintf_s, _vwprintf_s_l

Writes formatted output by using a pointer to a list of arguments. These versions of vprintf, _vprintf_l, vwprintf, _vwprintf_l have security enhancements, as described in Security features in the CRT.

Syntax

int vprintf_s(
   const char *format,
   va_list argptr
);
int _vprintf_s_l(
   const char *format,
   _locale_t locale,
   va_list argptr
);
int vwprintf_s(
   const wchar_t *format,
   va_list argptr
);
int _vwprintf_s_l(
   const wchar_t *format,
   _locale_t locale,
   va_list argptr
);

Parameters

format
Format specification.

argptr
Pointer to list of arguments.

locale
The locale to use.

For more information, see Format specification syntax.

Return value

vprintf_s and vwprintf_s return the number of characters written, not including the terminating null character, or a negative value if an output error occurs. If 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 errno, _doserrno, _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 stdout.

The secure versions of these functions differ from vprintf and vwprintf only in that the secure versions check that the format string contains valid formatting characters.

vwprintf_s is the wide-character version of vprintf_s; the two functions behave identically if the stream is opened in ANSI mode. vprintf_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. Starting in Windows 10 version 2004 (build 19041), the printf family of functions prints exactly representable floating point numbers according to the IEEE 754 rules for rounding. In previous versions of Windows, exactly representable floating point numbers ending in '5' would always round up. IEEE 754 states that they must round to the closest even digit (also known as "Banker's Rounding"). For example, both printf("%1.0f", 1.5) and printf("%1.0f", 2.5) should round to 2. Previously, 1.5 would round to 2 and 2.5 would round to 3. This change only affects exactly representable numbers. For example, 2.35 (which, when represented in memory, is closer to 2.35000000000000008) continues to round up to 2.4. Rounding done by these functions now also respects the floating point rounding mode set by fesetround. Previously, rounding always chose FE_TONEAREST behavior. This change only affects programs built using Visual Studio 2019 version 16.2 and later. To use the legacy floating point rounding behavior, link with 'legacy_stdio_float_rounding.obj`.

Generic-text routine mappings

TCHAR.H routine	_UNICODE and _MBCS not defined	_MBCS defined	_UNICODE defined
_vtprintf_s	vprintf_s	vprintf_s	vwprintf_s
_vtprintf_s_l	_vprintf_s_l	_vprintf_s_l	_vwprintf_s_l

Requirements

Routine	Required header	Optional headers
vprintf_s, _vprintf_s_l	<stdio.h> and <stdarg.h>	<varargs.h>*
vwprintf_s, _vwprintf_s_l	<stdio.h> or <wchar.h>, and <stdarg.h>	<varargs.h>*

* Required for UNIX V compatibility.

The console isn't supported in Universal Windows Platform (UWP) apps. The standard stream handles that are associated with the console, stdin, stdout, and stderr, must be redirected before C run-time functions can use them in UWP apps. For more compatibility information, see Compatibility.

See also

Stream I/O
vprintf functions
fprintf, _fprintf_l, fwprintf, _fwprintf_l
printf, _printf_l, wprintf, _wprintf_l
sprintf, _sprintf_l, swprintf, _swprintf_l, __swprintf_l
va_arg, va_copy, va_end, va_start