Next: File Owner, Previous: Reading Attributes, Up: File Attributes [Contents][Index]
The file mode, stored in the st_mode
field of the file
attributes, contains two kinds of information: the file type code, and
the access permission bits. This section discusses only the type code,
which you can use to tell whether the file is a directory, socket,
symbolic link, and so on. For details about access permissions see
Permission Bits.
There are two ways you can access the file type information in a file mode. Firstly, for each file type there is a predicate macro which examines a given file mode and returns whether it is of that type or not. Secondly, you can mask out the rest of the file mode to leave just the file type code, and compare this against constants for each of the supported file types.
All of the symbols listed in this section are defined in the header file sys/stat.h.
The following predicate macros test the type of a file, given the value
m which is the st_mode
field returned by stat
on
that file:
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This macro returns non-zero if the file is a directory.
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This macro returns non-zero if the file is a character special file (a device like a terminal).
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This macro returns non-zero if the file is a block special file (a device like a disk).
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This macro returns non-zero if the file is a regular file.
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This macro returns non-zero if the file is a FIFO special file, or a pipe. See Pipes and FIFOs.
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This macro returns non-zero if the file is a symbolic link. See Symbolic Links.
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This macro returns non-zero if the file is a socket. See Sockets.
An alternate non-POSIX method of testing the file type is supported for
compatibility with BSD. The mode can be bitwise AND-ed with
S_IFMT
to extract the file type code, and compared to the
appropriate constant. For example,
S_ISCHR (mode)
is equivalent to:
((mode & S_IFMT) == S_IFCHR)
This is a bit mask used to extract the file type code from a mode value.
These are the symbolic names for the different file type codes:
S_IFDIR
This is the file type constant of a directory file.
S_IFCHR
This is the file type constant of a character-oriented device file.
S_IFBLK
This is the file type constant of a block-oriented device file.
S_IFREG
This is the file type constant of a regular file.
S_IFLNK
This is the file type constant of a symbolic link.
S_IFSOCK
This is the file type constant of a socket.
S_IFIFO
This is the file type constant of a FIFO or pipe.
The POSIX.1b standard introduced a few more objects which possibly can
be implemented as object in the filesystem. These are message queues,
semaphores, and shared memory objects. To allow differentiating these
objects from other files the POSIX standard introduces three new test
macros. But unlike the other macros it does not take the value of the
st_mode
field as the parameter. Instead they expect a pointer to
the whole struct stat
structure.
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
If the system implement POSIX message queues as distinct objects and the file is a message queue object, this macro returns a non-zero value. In all other cases the result is zero.
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
If the system implement POSIX semaphores as distinct objects and the file is a semaphore object, this macro returns a non-zero value. In all other cases the result is zero.
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
If the system implement POSIX shared memory objects as distinct objects and the file is a shared memory object, this macro returns a non-zero value. In all other cases the result is zero.
Next: File Owner, Previous: Reading Attributes, Up: File Attributes [Contents][Index]