access()

Check to see if a file or directory can be accessed

Synopsis:

#include <unistd.h>

int access( const char * path,
            int amode );

Arguments:

path

The path to the file or directory that you want to access.

amode

The access mode you want to check. This must be either:

F_OK — test for file existence.

or a bitwise ORing of the following access permissions to be checked, as defined in the header <unistd.h>:

R_OK — test for read permission.
W_OK — test for write permission.
X_OK — for a directory, test for search permission. Otherwise, test for execute permission.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The access() function checks to see if the file or directory specified by path exists and if it can be accessed with the file access permissions given by amode. However, unlike other functions (open() for example), it uses the real user ID and real group ID in place of the effective user and group IDs.

Returns:

0: The file or directory exists and can be accessed with the specified mode.
-1: An error occurred (errno is set).

Errors:

EACCES: The permissions specified by amode are denied, or search permission is denied on a component of the path prefix.
EINTR: This function was interrupted by a signal.
EINVAL: An invalid value was specified for amode.
ELOOP: Too many levels of symbolic links or prefixes.
ENAMETOOLONG: The length of the path string exceeds PATH_MAX, or a pathname component is longer than NAME_MAX.
ENOENT: A component of the path isn't valid.
ENOSYS: The access() function isn't implemented for the filesystem specified in path.
ENOTDIR: A component of the path prefix isn't a directory.
EROFS: Write access was requested for a file residing on a read-only file system.

Examples:

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

int main( int argc, char **argv )
  {
    if( argc!= 2 ) {
      fprintf( stderr, 
        "use: readable <filename>\n" );
      return EXIT_FAILURE;
    }

    if( !access( argv[1], R_OK ) ) {
      printf( "ok to read %s\n", argv[1] );
      return EXIT_SUCCESS;
    } else {
      perror( argv[1] );
      return EXIT_FAILURE;
    }
  }

Classification:

POSIX 1003.1

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	Yes
Thread	Yes