"Dave R. Meyers" wrote:
>
> I am unfamialer with teh access function, and cannot find any referances to
> it in any of my C/C++ books.
It is a POSIX system call, not an ANSI C function.
man 2 access
-----------------------------------------------------------------
ACCESS(2) System calls ACCESS(2)
NAME
access - check user's permissions for a file
SYNOPSIS
#include <unistd.h>
int access(const char *pathname, int mode);
DESCRIPTION
access checks whether the process would be allowed to
read, write or test for existence of the file (or other
file system object) whose name is pathname. If pathname
is a symbolic link permissions of the file referred to by
this symbolic link are tested.
mode is a mask consisting of one or more of R_OK, W_OK,
X_OK and F_OK.
R_OK, W_OK and X_OK request checking whether the file
exists and has read, write and execute permissions,
respectively. F_OK just requests checking for the exis
tence of the file.
The tests depend on the permissions of the directories
occurring in the path to the file, as given in pathname,
and on the permissions of directories and files referred
to by symbolic links encountered on the way.
The check is done with the process's real uid and gid,
rather than with the effective ids as is done when actu
ally attempting an operation. This is to allow set-UID
programs to easily determine the invoking user's author
ity.
Only access bits are checked, not the file type or con
tents. Therefore, if a directory is found to be
"writable," it probably means that files can be created in
the directory, and not that the directory can be written
as a file. Similarly, a DOS file may be found to be "exe
cutable," but the execve(2) call will still fail.
RETURN VALUE
On success (all requested permissions granted), zero is
returned. On error (at least one bit in mode asked for a
permission that is denied, or some other error occurred),
-1 is returned, and errno is set appropriately.
ERRORS
EACCES The requested access would be denied to the file or
search permission is denied to one of the directo
ries in pathname.
EROFS Write permission was requested for a file on a
read-only filesystem.
EFAULT pathname points outside your accessible address
space.
EINVAL mode was incorrectly specified.
ENAMETOOLONG
pathname is too long.
ENOENT A directory component in pathname would have been
accessible but does not exist or was a dangling
symbolic link.
ENOTDIR
A component used as a directory in pathname is not,
in fact, a directory.
ENOMEM Insufficient kernel memory was available.
ELOOP Too many symbolic links were encountered in resolv
ing pathname.
EIO An I/O error occurred.
RESTRICTIONS
access returns an error if any of the access types in the
requested call fails, even if other types might be suc
cessful.
access may not work correctly on NFS file systems with UID
mapping enabled, because UID mapping is done on the server
and hidden from the client, which checks permissions.
Using access to check if a user is authorized to e.g. open
a file before actually doing so using open(2) creates a
security hole, because the user might exploit the short
time interval between checking and opening the file to
manipulate it.
CONFORMING TO
SVID, AT&T, POSIX, X/OPEN, BSD 4.3
SEE ALSO
stat(2), open(2), chmod(2), chown(2), setuid(2), setgid(2)
-----------------------------------------------------------------
> The above function works fine, but I need to know if it is checking the
> first 4 leters or teh last 4 leters of teh file name. Or just what teh 04
> is for?
Are you developing under Linux or Windows? I don't know what the
Windows version of access would do. The 04 is the octal 4 and
stands for read access.
Florian.
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