_access, _waccess

發行項
06/05/2017

The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.

The latest version of this topic can be found at _access, _waccess.

Determines if a file is read-only or not. More secure versions are available; see _access_s, _waccess_s.

Syntax

int _access(   
   const char *path,   
   int mode   
);  
int _waccess(   
   const wchar_t *path,   
   int mode   
);

Parameters

path
File or directory path.

mode
Read/write attribute.

Return Value

Each function returns 0 if the file has the given mode. The function returns –1 if the named file does not exist or does not have the given mode; in this case, errno is set as shown in the following table.

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 about these and other return codes, see _doserrno, errno, _sys_errlist, and _sys_nerr.

Remarks

When used with files, the _access function determines whether the specified file or directory exists and has the attributes specified by the value of mode. When used with directories, _access 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-only
04	Read-only
06	Read and write

This function only checks whether the file and directory are read-only or not, it does not check the filesystem security settings. For that you need an access token. For more information on filesystem security, see Access Tokens. An ATL class exists to provide this functionality; see CAccessToken Class.

_waccess is a wide-character version of _access; the path argument to _waccess is a wide-character string. _waccess and _access behave identically otherwise.

This function validates its 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, the function sets errno to EINVAL and returns -1.

Generic-Text Routine Mappings

Tchar.h routine	_UNICODE and _MBCS not defined	_MBCS defined	_UNICODE defined
`_taccess`	`_access`	`_access`	`_waccess`

Requirements

Routine	Required header	Optional headers
`_access`	<io.h>	<errno.h>
`_waccess`	<wchar.h> or <io.h>	<errno.h>

Example

The following example uses _access to check the file named crt_ACCESS.C to see whether it exists and whether writing is allowed.

// crt_access.c  
// compile with: /W1  
// This example uses _access to check the file named  
// crt_ACCESS.C to see if it exists and if writing is allowed.  
  
#include  <io.h>  
#include  <stdio.h>  
#include  <stdlib.h>  
  
int main( void )  
{  
    // Check for existence.  
    if( (_access( "crt_ACCESS.C", 0 )) != -1 )  
    {  
        printf_s( "File crt_ACCESS.C exists.\n" );  
  
        // Check for write permission.  
        // Assume file is read-only.  
        if( (_access( "crt_ACCESS.C", 2 )) == -1 )  
            printf_s( "File crt_ACCESS.C does not have write permission.\n" );  
    }  
}

File crt_ACCESS.C exists.  
File crt_ACCESS.C does not have write permission.

.NET Framework Equivalent

System.IO.FileAccess

共用方式為