sprintf, _sprintf_l, swprintf, _swprintf_l, __swprintf_l

Article
04/22/2008

Write formatted data to a string. More secure versions of some of these functions are available; see sprintf_s, _sprintf_s_l, swprintf_s, _swprintf_s_l. swprintf and _swprintf_l do not have a more secure version because they take a count parameter.

int sprintf(
   char *buffer,
   const char *format [,
      argument] ... 
);
int _sprintf_l(
   char *buffer,
   const char *format,
   locale_t locale [,
      argument] ... 
);
int swprintf(
   wchar_t *buffer,
   size_t count,
   const wchar_t *format [,
      argument]...
);
int _swprintf_l(
   wchar_t *buffer,
   size_t count,
   const wchar_t *format,
   locale_t locale [,
      argument] ... 
);
int __swprintf_l(
   wchar_t *buffer,
   const wchar_t *format,
   locale_t locale [,
      argument] ... 
);
template <size_t size>
int sprintf(
   char (&buffer)[size],
   const char *format [,
      argument] ... 
); // C++ only
template <size_t size>
int _sprintf_l(
   char (&buffer)[size],
   const char *format,
   locale_t locale [,
      argument] ... 
); // C++ only
template <size_t size>
int swprintf(
   wchar_t (&buffer)[size],
   size_t count,
   const wchar_t *format [,
      argument]...
); // C++ only
template <size_t size>
int _swprintf_l(
   wchar_t (&buffer)[size],
   size_t count,
   const wchar_t *format,
   locale_t locale [,
      argument] ... 
); // C++ only

Parameters

buffer
Storage location for output
count
Maximum number of characters to store in the Unicode version of this function.
format
Format-control string
argument
Optional arguments
locale
The locale to use.

For more information, see Format Specifications.

Return Value

The number of characters written, or –1 if an error occurred. If buffer or format is a null pointer, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, these functions return -1 and set errno to EINVAL.

sprintf returns the number of bytes stored in buffer, not counting the terminating null character. swprintfreturns the number of wide characters stored in buffer, not counting the terminating null wide character.

Remarks

The sprintf function formats and stores a series of characters and values in buffer. Each argument (if any) is converted and output according to the corresponding format specification in format. The format consists of ordinary characters and has the same form and function as the format argument for printf. A null character is appended after the last character written. If copying occurs between strings that overlap, the behavior is undefined.

Security Note:
Using sprintf, there is no way to limit the number of characters written, which means that code using sprintf is susceptible to buffer overruns. Consider using the related function _snprintf, which specifies a maximum number of characters to be written to buffer, or use _scprintf to determine how large a buffer is required. Also, ensure that format is not a user-defined string.

swprintf is a wide-character version of sprintf; the pointer arguments to swprintf are wide-character strings. Detection of encoding errors in swprintf may differ from that in sprintf. swprintf and fwprintf behave identically except that swprintf writes output to a string rather than to a destination of type FILE, and swprintf requires the countparameter to specify the maximum number of characters to be written. 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.

In Visual C++ 2005, swprintf 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. In a future version, the old behavior may be removed, 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 & _MBCS not defined	_MBCS defined	_UNICODE defined
_stprintf	sprintf	sprintf	swprintf
_stprintf_l	_sprintf_l	_sprintf_l	__swprintf_l

Requirements

Routine	Required header
sprintf, _sprintf_l	<stdio.h>
swprintf, _swprintf_l	<stdio.h> or <wchar.h>

For additional compatibility information, see Compatibility in the Introduction.

Example

// crt_sprintf.c
// compile with: /W3
// This program uses sprintf to format various
// data and place them in the string named buffer.

#include <stdio.h>

int main( void )
{
   char  buffer[200], s[] = "computer", c = 'l';
   int   i = 35, j;
   float fp = 1.7320534f;

   // Format and print various data: 
   j  = sprintf( buffer,     "   String:    %s\n", s ); // C4996
   j += sprintf( buffer + j, "   Character: %c\n", c ); // C4996
   j += sprintf( buffer + j, "   Integer:   %d\n", i ); // C4996
   j += sprintf( buffer + j, "   Real:      %f\n", fp );// C4996
   // Note: sprintf is deprecated; consider using sprintf_s instead

   printf( "Output:\n%s\ncharacter count = %d\n", buffer, j );
}

Output:
   String:    computer
   Character: l
   Integer:   35
   Real:      1.732053

character count = 79

// crt_swprintf.c
// wide character example
// also demonstrates swprintf returning error code
#include <stdio.h>

int main( void )
{
   wchar_t buf[100];
   int len = swprintf( buf, 100, L"%s", L"Hello world" );
   printf( "wrote %d characters\n", len );
   len = swprintf( buf, 100, L"%s", L"Hello\xffff world" );
   // swprintf fails because string contains WEOF (\xffff)
   printf( "wrote %d characters\n", len );
}

wrote 11 characters
wrote -1 characters

.NET Framework Equivalent

System::String::Format

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