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| <h4 class="subsection">14.9.3 Testing the Type of a File</h4> |
| |
| <p>The <dfn>file mode</dfn>, stored in the <code>st_mode</code> 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 |
| <a href="Permission-Bits.html#Permission-Bits">Permission Bits</a>. |
| |
| <p>There are two ways you can access the file type information in a file |
| mode. Firstly, for each file type there is a <dfn>predicate macro</dfn> |
| 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. |
| |
| <p>All of the symbols listed in this section are defined in the header file |
| <samp><span class="file">sys/stat.h</span></samp>. |
| <a name="index-sys_002fstat_002eh-1511"></a> |
| The following predicate macros test the type of a file, given the value |
| <var>m</var> which is the <code>st_mode</code> field returned by <code>stat</code> on |
| that file: |
| |
| <!-- sys/stat.h --> |
| <!-- POSIX --> |
| <div class="defun"> |
| — Macro: int <b>S_ISDIR</b> (<var>mode_t m</var>)<var><a name="index-S_005fISDIR-1512"></a></var><br> |
| <blockquote><p>This macro returns non-zero if the file is a directory. |
| </p></blockquote></div> |
| |
| <!-- sys/stat.h --> |
| <!-- POSIX --> |
| <div class="defun"> |
| — Macro: int <b>S_ISCHR</b> (<var>mode_t m</var>)<var><a name="index-S_005fISCHR-1513"></a></var><br> |
| <blockquote><p>This macro returns non-zero if the file is a character special file (a |
| device like a terminal). |
| </p></blockquote></div> |
| |
| <!-- sys/stat.h --> |
| <!-- POSIX --> |
| <div class="defun"> |
| — Macro: int <b>S_ISBLK</b> (<var>mode_t m</var>)<var><a name="index-S_005fISBLK-1514"></a></var><br> |
| <blockquote><p>This macro returns non-zero if the file is a block special file (a device |
| like a disk). |
| </p></blockquote></div> |
| |
| <!-- sys/stat.h --> |
| <!-- POSIX --> |
| <div class="defun"> |
| — Macro: int <b>S_ISREG</b> (<var>mode_t m</var>)<var><a name="index-S_005fISREG-1515"></a></var><br> |
| <blockquote><p>This macro returns non-zero if the file is a regular file. |
| </p></blockquote></div> |
| |
| <!-- sys/stat.h --> |
| <!-- POSIX --> |
| <div class="defun"> |
| — Macro: int <b>S_ISFIFO</b> (<var>mode_t m</var>)<var><a name="index-S_005fISFIFO-1516"></a></var><br> |
| <blockquote><p>This macro returns non-zero if the file is a FIFO special file, or a |
| pipe. See <a href="Pipes-and-FIFOs.html#Pipes-and-FIFOs">Pipes and FIFOs</a>. |
| </p></blockquote></div> |
| |
| <!-- sys/stat.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Macro: int <b>S_ISLNK</b> (<var>mode_t m</var>)<var><a name="index-S_005fISLNK-1517"></a></var><br> |
| <blockquote><p>This macro returns non-zero if the file is a symbolic link. |
| See <a href="Symbolic-Links.html#Symbolic-Links">Symbolic Links</a>. |
| </p></blockquote></div> |
| |
| <!-- sys/stat.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Macro: int <b>S_ISSOCK</b> (<var>mode_t m</var>)<var><a name="index-S_005fISSOCK-1518"></a></var><br> |
| <blockquote><p>This macro returns non-zero if the file is a socket. See <a href="Sockets.html#Sockets">Sockets</a>. |
| </p></blockquote></div> |
| |
| <p>An alternate non-POSIX method of testing the file type is supported for |
| compatibility with BSD. The mode can be bitwise AND-ed with |
| <code>S_IFMT</code> to extract the file type code, and compared to the |
| appropriate constant. For example, |
| |
| <pre class="smallexample"> S_ISCHR (<var>mode</var>) |
| </pre> |
| <p class="noindent">is equivalent to: |
| |
| <pre class="smallexample"> ((<var>mode</var> & S_IFMT) == S_IFCHR) |
| </pre> |
| <!-- sys/stat.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: int <b>S_IFMT</b><var><a name="index-S_005fIFMT-1519"></a></var><br> |
| <blockquote><p>This is a bit mask used to extract the file type code from a mode value. |
| </p></blockquote></div> |
| |
| <p>These are the symbolic names for the different file type codes: |
| |
| <dl> |
| <!-- sys/stat.h --> |
| <!-- BSD --> |
| <dt><code>S_IFDIR</code><dd><a name="index-S_005fIFDIR-1520"></a>This is the file type constant of a directory file. |
| |
| <!-- sys/stat.h --> |
| <!-- BSD --> |
| <br><dt><code>S_IFCHR</code><dd><a name="index-S_005fIFCHR-1521"></a>This is the file type constant of a character-oriented device file. |
| |
| <!-- sys/stat.h --> |
| <!-- BSD --> |
| <br><dt><code>S_IFBLK</code><dd><a name="index-S_005fIFBLK-1522"></a>This is the file type constant of a block-oriented device file. |
| |
| <!-- sys/stat.h --> |
| <!-- BSD --> |
| <br><dt><code>S_IFREG</code><dd><a name="index-S_005fIFREG-1523"></a>This is the file type constant of a regular file. |
| |
| <!-- sys/stat.h --> |
| <!-- BSD --> |
| <br><dt><code>S_IFLNK</code><dd><a name="index-S_005fIFLNK-1524"></a>This is the file type constant of a symbolic link. |
| |
| <!-- sys/stat.h --> |
| <!-- BSD --> |
| <br><dt><code>S_IFSOCK</code><dd><a name="index-S_005fIFSOCK-1525"></a>This is the file type constant of a socket. |
| |
| <!-- sys/stat.h --> |
| <!-- BSD --> |
| <br><dt><code>S_IFIFO</code><dd><a name="index-S_005fIFIFO-1526"></a>This is the file type constant of a FIFO or pipe. |
| </dl> |
| |
| <p>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 |
| <code>st_mode</code> field as the parameter. Instead they expect a pointer to |
| the whole <code>struct stat</code> structure. |
| |
| <!-- sys/stat.h --> |
| <!-- POSIX --> |
| <div class="defun"> |
| — Macro: int <b>S_TYPEISMQ</b> (<var>struct stat *s</var>)<var><a name="index-S_005fTYPEISMQ-1527"></a></var><br> |
| <blockquote><p>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. |
| </p></blockquote></div> |
| |
| <!-- sys/stat.h --> |
| <!-- POSIX --> |
| <div class="defun"> |
| — Macro: int <b>S_TYPEISSEM</b> (<var>struct stat *s</var>)<var><a name="index-S_005fTYPEISSEM-1528"></a></var><br> |
| <blockquote><p>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. |
| </p></blockquote></div> |
| |
| <!-- sys/stat.h --> |
| <!-- POSIX --> |
| <div class="defun"> |
| — Macro: int <b>S_TYPEISSHM</b> (<var>struct stat *s</var>)<var><a name="index-S_005fTYPEISSHM-1529"></a></var><br> |
| <blockquote><p>If the system implement POSIX shared memory objects as distinct objects |
| and the file is an shared memory object, this macro returns a non-zero |
| value. In all other cases the result is zero. |
| </p></blockquote></div> |
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