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sscanf_s, _sscanf_s_l, swscanf_s, _swscanf_s_l

Read formatted data from a string. These are versions of sscanf, _sscanf_l, swscanf, _swscanf_l with security enhancements as described in Security Features in the CRT.

int sscanf_s(
   const char *buffer,
   const char *format [,
   argument ] ...
int _sscanf_s_l(
   const char *buffer,
   const char *format,
   locale_t locale [,
   argument ] ...
int swscanf_s(
   const wchar_t *buffer,
   const wchar_t *format [,
   argument ] ...
int _swscanf_s_l(
   const wchar_t *buffer,
   const wchar_t *format,
   locale_t locale [,
   argument ] ...


Stored data


Format-control string. For more information, see Format Specifications.


Optional arguments


The locale to use

Each of these functions returns the number of fields successfully converted and assigned; the return value does not include fields that were read but not assigned. A return value of 0 indicates that no fields were assigned. The return value is EOF for an error or if the end of the string is reached before the first conversion.

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

For information on these and other error codes, see _doserrno, errno, _sys_errlist, and _sys_nerr.

The sscanf_s function reads data from buffer into the location given by each argument. The arguments after the format string specify pointers to variables with a type that corresponds to a type specifier in format. Unlike the less secure version sscanf, a buffer size parameter is required when using the type field characters c, C, s, S and [. The buffer size in characters must be supplied as an additional parameter after each buffer which requires it. For more information, see scanf_s, _scanf_s_l, wscanf_s, _wscanf_s_l and scanf Type Field Characters.


The size parameter is of type unsigned, not size_t.

The format argument controls the interpretation of the input fields and has the same form and function as the format argument for the scanf_s function. If copying takes place between strings that overlap, the behavior is undefined.

swscanf_s is a wide-character version of sscanf_s; the arguments to swscanf_s are wide-character strings. sscanf_s does not handle multibyte hexadecimal characters. swscanf_s does not handle Unicode full width hexadecimal or "compatibility zone" characters. Otherwise, swscanf_s and sscanf_s behave identically.

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.

Generic-Text Routine Mappings

TCHAR.H routine

_UNICODE & _MBCS not defined

_MBCS defined

_UNICODE defined










Required header

sscanf_s, _sscanf_s_l


swscanf_s, _swscanf_s_l

<stdio.h> or <wchar.h>

For additional compatibility information, see Compatibility in the Introduction.

// crt_sscanf_s.c
// This program uses sscanf_s to read data items
// from a string named tokenstring, then displays them.

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

int main( void )
   char  tokenstring[] = "15 12 14...";
   char  s[81];
   char  c;
   int   i;
   float fp;

   // Input various data from tokenstring:
   // max 80 character string plus NULL terminator
   sscanf_s( tokenstring, "%s", s, _countof(s) );
   sscanf_s( tokenstring, "%c", &c, sizeof(char) );
   sscanf_s( tokenstring, "%d", &i );
   sscanf_s( tokenstring, "%f", &fp );

   // Output the data read
   printf_s( "String    = %s\n", s );
   printf_s( "Character = %c\n", c );
   printf_s( "Integer:  = %d\n", i );
   printf_s( "Real:     = %f\n", fp );
String    = 15
Character = 1
Integer:  = 15
Real:     = 15.000000