_vsprintf_p, _vsprintf_p_l, _vswprintf_p, _vswprintf_p_l

Write formatted output using a pointer to a list of arguments, with the ability to specify the order in which the arguments are used.

Syntax

int _vsprintf_p(
   char *buffer,
   size_t sizeInBytes,
   const char *format,
   va_list argptr
);
int _vsprintf_p_l(
   char *buffer,
   size_t sizeInBytes,
   const char *format,
   _locale_t locale,
   va_list argptr
);
int _vswprintf_p(
   wchar_t *buffer,
   size_t count,
   const wchar_t *format,
   va_list argptr
);
int _vswprintf_p_l(
   wchar_t *buffer,
   size_t count,
   const wchar_t *format,
   _locale_t locale,
   va_list argptr
);

Parameters

buffer
Storage location for output.

sizeInBytes
Size of buffer in characters.

count
Maximum number of characters to store, in the UNICODE version of this function.

format
Format specification.

argptr
Pointer to list of arguments.

locale
The locale to use.

Return value

_vsprintf_p and _vswprintf_p return the number of characters written, not including the terminating null character, or a negative value if an output error occurs.

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.

These functions differ from the vsprintf_s and vswprintf_s only in that they support positional parameters. For more information, see printf_p Positional Parameters.

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.

If the buffer or format parameters are NULL pointers, if count is zero, 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.

Important

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
_vstprintf_p	_vsprintf_p	_vsprintf_p	_vswprintf_p
_vstprintf_p_l	_vsprintf_p_l	_vsprintf_p_l	_vswprintf_p_l

Requirements

Routine	Required header	Optional headers
_vsprintf_p, _vsprintf_p_l	<stdio.h> and <stdarg.h>	<varargs.h>*
_vswprintf_p, _vswprintf_p_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_p.c
// This program uses vsprintf_p to write to a buffer.
// The size of the buffer is determined by _vscprintf_p.

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

void example( char * format, ... )
{
    va_list  args;
    int      len;
    char     *buffer = NULL;

    va_start( args, format );

    // _vscprintf doesn't count the
    // null terminating string so we add 1.
    len = _vscprintf_p( format, args ) + 1;

    // Allocate memory for our buffer
    buffer = (char*)malloc( len * sizeof(char) );
    if (buffer)
    {
        _vsprintf_p( buffer, len, format, args );
        puts( buffer );
        free( buffer );
    }
    va_end( args );
}

int main( void )
{
    // First example
    example( "%2$d %1$c %3$d", '<', 123, 456 );

    // Second example
    example( "%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