access

Name

access - checks user's permissions for a file

Library

libc.lib

Synopsis

#include <unistd.h>

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

Return values

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

Detailed description

The access system calls check the accessibility of the file named by the path argument for the access permissions indicated by the mode argument. The value of mode is either the bitwise-inclusive OR of the access permissions to be checked (R_OK for read permission, W_OK for write permission, and X_OK for execute/search permission), or the existence test (F_OK.)

For additional information, see the File Access Permission section of intro . X_OK, the file may not actually have execute permission bits set. Likewise for R_OK and W_OK.

Note that as execute-bit for file is not supported hence access system call for X_OK is undefined.

Examples

/**
 * Detailed description: This sample code checks read-ok accessibility of file Example.c
 *
 * Precondtions: Example.txt file should be present in working directory.
**/
#include <unistd.h>
int main()
{
  if(access("Example.c" ,R_OK)  < 0)  
  {
    printf("Read operation on the file is not permitted \n") ;
    return -1 ;
  }
  printf("Read operation permitted on Example.c file \n") ;
  return 0 ;
}

Output

Read operation permitted on Example.c file

Errors

Access to the file is denied if:

[`ENOTDIR`]
	A component of the path prefix is not a directory.
[`ENAMETOOLONG`]
	A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters (Not supported).
[`ENOENT`]
	The named file does not exist.
[`ELOOP`]
	Too many symbolic links were encountered in translating the pathname (Not supported).
[`EROFS`]
	Write access is requested for a file on a read-only file system (Not supported).
[`ETXTBSY`]
	Write access is requested for a pure procedure (shared text) file presently being executed(Not supported).
[`EACCES`]
	Permission bits of the file mode do not permit the requested access, or search permission is denied on a component of the path prefix.
[`EFAULT`]
	The path argument points outside the process’s allocated address space (Not supported)
[`EIO`]

An I/O error occurred while reading from or writing to the file system(Not supported)

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