sprintf, _sprintf_l, swprintf, _swprintf, _swprintf_l, __swprintf_l

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. The secure versions of swprintf and _swprintf_l take the size of the buffer as a parameter.

Syntax

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(
   wchar_t *buffer,
   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

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 specification syntax.

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. swprintf returns 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.

Important

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 write to buffer, or use _scprintf to determine how large a buffer is required. Also, ensure that format is not a user-defined string.

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`.

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 sprintf. swprintf and fwprintf behave identically except swprintf writes output to a string rather than to a destination of type FILE, and swprintf requires the count parameter to specify the maximum number of characters to write. The versions of these functions with the _l suffix are identical except they use the locale parameter passed in instead of the current thread locale.

Before the signature for swprintf was standardized, a version shipped in an older Microsoft C runtime library that didn't take the character count parameter. The older version is still available in the Microsoft C runtime library, but it's deprecated and was renamed _swprintf(). For code that was written against the older signature, define _CRT_NON_CONFORMING_SWPRINTFS, which maps calls to swprintf to _swprintf. 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 and _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, _swprintf_l	<stdio.h> or <wchar.h>

For more compatibility information, see Compatibility.

Example: Use sprintf to format data

// 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

Example: Error code handling

// 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

See also

Stream I/O
fprintf, _fprintf_l, fwprintf, _fwprintf_l
printf, _printf_l, wprintf, _wprintf_l
scanf, _scanf_l, wscanf, _wscanf_l
sscanf, _sscanf_l, swscanf, _swscanf_l
vprintf functions