sscanf_s, _sscanf_s_l, swscanf_s, _swscanf_s_l

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06/05/2017

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The latest version of this topic can be found at sscanf_s, _sscanf_s_l, swscanf_s, _swscanf_s_l.

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

Syntax

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 ] ...  
);

Parameters

buffer
Stored data

format
Format-control string. For more information, see Format Specification Fields: scanf and wscanf Functions.

argument
Optional arguments

locale
The locale to use

Return Value

Each of these functions returns the number of fields that are 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 about these and other error codes, see errno, _doserrno, _sys_errlist, and _sys_nerr.

Remarks

The sscanf_s function reads data from buffer into the location that's given by each argument. The arguments after the format string specify pointers to variables that have a type that corresponds to a type specifier in format. Unlike the less secure version sscanf, a buffer size parameter is required when you use the type field characters c, C, s, S, or string control sets that are enclosed in []. The buffer size in characters must be supplied as an additional parameter immediately after each buffer parameter that requires it. For example, if you are reading into a string, the buffer size for that string is passed as follows:

wchar_t ws[10];

swscanf_s(in_str, L"%9s", ws, (unsigned)_countof(ws)); // buffer size is 10, width specification is 9

The buffer size includes the terminating null. A width specification field may be used to ensure that the token that's read in will fit into the buffer. If no width specification field is used, and the token read in is too big to fit in the buffer, nothing is written to that buffer.

In the case of characters, a single character may be read as follows:

wchar_t wc;

swscanf_s(in_str, L"%c", &wc, 1);

This example reads a single character from the input string and then stores it in a wide-character buffer. When you read multiple characters for non-null terminated strings, unsigned integers are used as the width specification and the buffer size.

char c[4];

sscanf_s(input, "%4c", &c, (unsigned)_countof(c)); // not null terminated

For more information, see scanf_s, _scanf_s_l, wscanf_s, _wscanf_s_l and scanf Type Field Characters.

Note

The size parameter is of type unsigned, not size_t. When compiling for 64-bit targets, use a static cast to convert _countof or sizeof results to the correct size.

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 occurs 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 that have the _l suffix are identical except that they use the locale parameter that's passed in instead of the current thread locale.

Generic-Text Routine Mappings

TCHAR.H routine	_UNICODE & _MBCS not defined	_MBCS defined	_UNICODE defined
`_stscanf_s`	`sscanf_s`	`sscanf_s`	`swscanf_s`
`_stscanf_s_l`	`_sscanf_s_l`	`_sscanf_s_l`	`_swscanf_s_l`

Requirements

Routine	Required header
`sscanf_s`, `_sscanf_s_l`	<stdio.h>
`swscanf_s`, `_swscanf_s_l`	<stdio.h> or <wchar.h>

For additional compatibility information, see Compatibility.

Example

// 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, (unsigned)_countof(s) );  
   sscanf_s( tokenstring, "%c", &c, (unsigned)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

.NET Framework Equivalent

See Parse methods, such as System::Double::Parse.

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