_access_s, _waccess_s

Artikel
02/01/2013

Determines file read/write permissions. This is a version of _access, _waccess with security enhancements as described in Security Features in the CRT.

errno_t _access_s( 
   const char *path, 
   int mode 
);
errno_t _waccess_s( 
   const wchar_t *path, 
   int mode 
);

Parameters

path
File or directory path.
mode
Permission setting.

Return Value

Each function returns 0 if the file has the given mode. The function returns an error code if the named file does not exist or is not accessible in the given mode. In this case, the function returns an error code from the set as follows and also sets errno to the same value.

EACCES
Access denied. The file's permission setting does not allow specified access.
ENOENT
File name or path not found.
EINVAL
Invalid parameter.

For more information, see errno, _doserrno, _sys_errlist, and _sys_nerr.

Remarks

When used with files, the _access_s function determines whether the specified file exists and can be accessed as specified by the value of mode. When used with directories, _access_s determines only whether the specified directory exists. In Windows 2000 and later operating systems, all directories have read and write access.

mode value	Checks file for
00	Existence only.
02	Write permission.
04	Read permission.
06	Read and write permission.

Permission to read or write the file is not enough to ensure the ability to open a file. For example, if a file is locked by another process, it might not be accessible even though _access_s returns 0.

_waccess_s is a wide-character version of _access_s, where the path argument to _waccess_s is a wide-character string. Otherwise, _waccess_s and _access_s behave identically.

These functions validate their parameters. If path is NULL or mode does not specify a valid mode, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, these functions set errno to EINVAL and return EINVAL.

Generic-Text Routine Mappings

Tchar.h routine	_UNICODE and _MBCS not defined	_MBCS defined	_UNICODE defined
_taccess_s	_access_s	_access_s	_waccess_s

Requirements

Routine	Required header	Optional header
_access_s	<io.h>	<errno.h>
_waccess_s	<wchar.h> or <io.h>	<errno.h>

Example

This example uses _access_s to check the file named crt_access_s.c to see whether it exists and whether writing is allowed.

// crt_access_s.c

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

int main( void )
{
    errno_t err = 0;

    // Check for existence. 
    if ((err = _access_s( "crt_access_s.c", 0 )) == 0 )
    {
        printf_s( "File crt_access_s.c exists.\n" );

        // Check for write permission. 
        if ((err = _access_s( "crt_access_s.c", 2 )) == 0 )
        {
            printf_s( "File crt_access_s.c does have "
                      "write permission.\n" );
        }
        else
        {
            printf_s( "File crt_access_s.c does not have "
                      "write permission.\n" );
        }
    }
    else
    {
        printf_s( "File crt_access_s.c does not exist.\n" );
    }
}

File crt_access_s.c exists.
File crt_access_s.c does not have write permission.

.NET Framework Equivalent

System.IO.FileAccess

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