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vsprintf, vswprintf

Visual Studio .NET 2003

Write formatted output using a pointer to a list of arguments.

int vsprintf(
   char *buffer,
   const char *format,
   va_list argptr 
); 
int vswprintf(
   wchar_t *buffer,
   const wchar_t *format,
   va_list argptr 
);
int vswprintf(
   wchar_t *buffer,
   size_t count,
   const wchar_t *format,
   va_list argptr 
); //  (C++ only)

Parameters

buffer: Storage location for output.
count: Maximum number of characters to store
format: Format specification.
argptr: Pointer to list of arguments.

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.

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.

Security Note There is no way to limit the number of characters written, which means that code using these functions 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.

Generic-Text Routine Mappings

TCHAR.H routine	_UNICODE & _MBCS not defined	_MBCS defined	_UNICODE defined
_vstprintf	vsprintf	vsprintf	vswprintf

Requirements

Routine	Required header	Optional headers	Compatibility
vsprintf	<stdio.h> and <stdarg.h>	<varargs.h>^*	ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP
vswprintf	<stdio.h> or <wchar.h>, and <stdarg.h>	<varargs.h>^*	ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP

* Required for UNIX V compatibility.

For additional compatibility information, see Compatibility in the Introduction.

Libraries

All versions of the C run-time libraries.

Example

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

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

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

   va_start( args, format );
   len = _vscprintf( format, args ) // _vscprintf doesn't count
                               + 1; // terminating '\0'
   buffer = malloc( len * sizeof(char) );
   vsprintf( buffer, format, args );
   printf( buffer );
   free( buffer );
}

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

Output

123 < 456
This is a string