vscanf_s, vwscanf_s

Reads formatted data from the standard input stream. These versions of vscanf, vwscanf have security enhancements, as described in Security features in the CRT.

Syntax

int vscanf_s(
   const char *format,
   va_list arglist
);
int vwscanf_s(
   const wchar_t *format,
   va_list arglist
);

Parameters

format
Format control string.

arglist
Variable argument list.

Return value

Returns the number of fields successfully converted and assigned; the return value doesn't 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-file character or the end-of-string character is encountered in the first attempt to read a character. If format is a NULL pointer, the invalid parameter handler is invoked, as described in Parameter validation. If execution is allowed to continue, vscanf_s and vwscanf_s return EOF and set errno to EINVAL.

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

Remarks

The vscanf_s function reads data from the standard input stream stdin and writes the data into the locations that are given by the arglist argument list. Each argument in the list must be a pointer to a variable of a type that corresponds to a type specifier in format. If copying occurs between strings that overlap, the behavior is undefined.

vwscanf_s is a wide-character version of vscanf_s; the format argument to vwscanf_s is a wide-character string. vwscanf_s and vscanf_s behave identically if the stream is opened in ANSI mode. vscanf_s doesn't support input from a UNICODE stream.

Unlike vscanf and vwscanf, vscanf_s and vwscanf_s require the buffer size to be specified for all input parameters of type c, C, s, S, or string control sets that are enclosed in []. The buffer size in characters is passed as another parameter immediately following the pointer to the buffer or variable. The buffer size in characters for a wchar_t string isn't the same as the size in bytes.

The buffer size includes the terminating null. You can use a width-specification field 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 large to fit in the buffer, nothing is written to that buffer.

For more information, see scanf Width Specification.

Generic-text routine mappings

For more information, see Format specification fields: scanf and wscanf functions.

Requirements

The console isn't supported in Universal Windows Platform (UWP) apps. The standard stream handles that are associated with the console, stdin, stdout, and stderr, must be redirected before C run-time functions can use them in UWP apps. For more compatibility information, see Compatibility.

Example

// crt_vscanf_s.c
// compile with: /W3
// This program uses the vscanf_s and vwscanf_s functions
// to read formatted input.

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

int call_vscanf_s(char *format, ...)
{
    int result;
    va_list arglist;
    va_start(arglist, format);
    result = vscanf_s(format, arglist);
    va_end(arglist);
    return result;
}

int call_vwscanf_s(wchar_t *format, ...)
{
    int result;
    va_list arglist;
    va_start(arglist, format);
    result = vwscanf_s(format, arglist);
    va_end(arglist);
    return result;
}

int main( void )
{
    int   i, result;
    float fp;
    char  c, s[81];
    wchar_t wc, ws[81];
    result = call_vscanf_s("%d %f %c %C %s %S", &i, &fp, &c, 1,
                           &wc, 1, s, _countof(s), ws, _countof(ws) );
    printf( "The number of fields input is %d\n", result );
    printf( "The contents are: %d %f %c %C %s %S\n", i, fp, c, wc, s, ws);
    result = call_vwscanf_s(L"%d %f %hc %lc %S %ls", &i, &fp, &c, 2,
                            &wc, 1, s, _countof(s), ws, _countof(ws) );
    wprintf( L"The number of fields input is %d\n", result );
    wprintf( L"The contents are: %d %f %C %c %hs %s\n", i, fp, c, wc, s, ws);
}

When this program is given the input in the example, it produces this output:

71 98.6 h z Byte characters
36 92.3 y n Wide characters

The number of fields input is 6
The contents are: 71 98.599998 h z Byte characters
The number of fields input is 6
The contents are: 36 92.300003 y n Wide characters

See also

Math and floating-point support
Stream I/O
Locale
printf, _printf_l, wprintf, _wprintf_l
scanf, _scanf_l, wscanf, _wscanf_l
scanf_s, _scanf_s_l, wscanf_s, _wscanf_s_l
vscanf, vwscanf