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vsscanf_s, vswscanf_s

Visual Studio 2013

Reads formatted data from a string. These versions of vsscanf, vswscanf have security enhancements, as described in Security Features in the CRT.

int vsscanf_s(
   const char *buffer,
   const char *format,
   va_list argptr
int vswscanf_s(
   const wchar_t *buffer,
   const wchar_t *format,
   va_list arglist


Stored data


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


Variable argument list.

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.

The vsscanf_s function reads data from buffer into the locations that are given by each argument in the arglist argument list. The arguments in the argument list specify pointers to variables that have a type that corresponds to a type specifier in format. Unlike the less secure version vsscanf, 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.

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.

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

Note Note

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 occurs between strings that overlap, the behavior is undefined.

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

Generic-Text Routine Mappings

TCHAR.H routine

_UNICODE & _MBCS not defined

_MBCS defined

_UNICODE defined






Required header




<stdio.h> or <wchar.h>

For additional compatibility information, see Compatibility.

// crt_vsscanf_s.c
// compile with: /W3
// This program uses vsscanf_s to read data items
// from a string named tokenstring, then displays them.

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

int call_vsscanf_s(char *tokenstring, char *format, ...)
    int result;
    va_list arglist;
    va_start(arglist, format);
    result = vsscanf_s(tokenstring, format, arglist);
    return result;

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:
    call_vsscanf_s(tokenstring, "%80s", s, _countof(s));
    call_vsscanf_s(tokenstring, "%c", &c, sizeof(char));
    call_vsscanf_s(tokenstring, "%d", &i);
    call_vsscanf_s(tokenstring, "%f", &fp);

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