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vsprintf, _vsprintf_l, vswprintf, _vswprintf_l, __vswprintf_l

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Write formatted output using a pointer to a list of arguments. More secure versions of these functions are available; see vsprintf_s, _vsprintf_s_l, vswprintf_s, _vswprintf_s_l.

Syntax

int vsprintf(
   char *buffer,
   const char *format,
   va_list argptr
);
int _vsprintf_l(
   char *buffer,
   const char *format,
   _locale_t locale,
   va_list argptr
);
int vswprintf(
   wchar_t *buffer,
   size_t count,
   const wchar_t *format,
   va_list argptr
);
int _vswprintf_l(
   wchar_t *buffer,
   size_t count,
   const wchar_t *format,
   _locale_t locale,
   va_list argptr
);
int __vswprintf_l(
   wchar_t *buffer,
   const wchar_t *format,
   _locale_t locale,
   va_list argptr
);
template <size_t size>
int vsprintf(
   char (&buffer)[size],
   const char *format,
   va_list argptr
); // C++ only
template <size_t size>
int _vsprintf_l(
   char (&buffer)[size],
   const char *format,
   _locale_t locale,
   va_list argptr
); // C++ only
template <size_t size>
int vswprintf(
   wchar_t (&buffer)[size],
   const wchar_t *format,
   va_list argptr
); // C++ only
template <size_t size>
int _vswprintf_l(
   wchar_t (&buffer)[size],
   const wchar_t *format,
   _locale_t locale,
   va_list argptr
); // C++ only

Parameters

buffer
Storage location for output.

count
Maximum number of characters to store, in the wide string versions of this function.

format
Format specification.

argptr
Pointer to list of arguments.

locale
The locale to use.

Return value

vsprintf and vswprintf return the number of characters written, not including the terminating NULL character, or a negative value if an output error occurs. If buffer or format is a NULL pointer, these functions invoke the invalid parameter handler, as described in Parameter validation. If execution is allowed to continue, these 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, and then formats and writes the given data to the memory pointed to by buffer.

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

Using vsprintf, there is no way to limit the number of characters written, which means that code using this function is susceptible to buffer overruns. Use _vsnprintf instead, or call _vscprintf to determine how large a buffer is needed. Also, 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`.

vswprintf conforms to the ISO C Standard, which requires the second parameter, count, of type size_t. To force the old nonstandard behavior, define _CRT_NON_CONFORMING_SWPRINTFS. The old behavior may not be in a future version, so code should be changed to use the new conformant behavior.

In C++, these functions have template overloads that invoke the newer, secure counterparts of these functions. For more information, see Secure template overloads.

Generic-text routine mappings

TCHAR.H routine _UNICODE and _MBCS not defined _MBCS defined _UNICODE defined
_vstprintf vsprintf vsprintf vswprintf
_vstprintf_l _vsprintf_l _vsprintf_l _vswprintf_l

Requirements

Routine Required header Optional headers
vsprintf, _vsprintf_l <stdio.h> and <stdarg.h> <varargs.h>*
vswprintf, _vswprintf_l <stdio.h> or <wchar.h>, and <stdarg.h> <varargs.h>*

* Required for UNIX V compatibility.

For more compatibility information, see Compatibility.

Example

// crt_vsprintf.c
// compile with: cl /W4 crt_vsprintf.c
// This program uses vsprintf to write to a buffer.
// The size of the buffer is determined by _vscprintf.

#define _CRT_SECURE_NO_WARNINGS
#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>

void test( char const * const format, ... )
{
    va_list args;
    int     len;
    char    *buffer;

    // retrieve the variable arguments
    va_start( args, format );

    len = _vscprintf( format, args ) // _vscprintf doesn't count
                                + 1; // terminating '\0'

    buffer = (char*)malloc( len * sizeof(char) );
    if ( 0 != buffer )
    {
        vsprintf( buffer, format, args ); // C4996
        // Note: vsprintf is deprecated; consider using vsprintf_s instead
        puts( buffer );

        free( buffer );
    }
    va_end( args );
}

int main( void )
{
   test( "%d %c %d", 123, '<', 456 );
   test( "%s", "This is a string" );
}

123 < 456
This is a string

See also

Stream I/O
vprintf functions
Format specification syntax: printf and wprintf 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