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| <h3 class="section">31.6 Limits on File System Capacity</h3> |
| |
| <p>The POSIX.1 standard specifies a number of parameters that describe the |
| limitations of the file system. It's possible for the system to have a |
| fixed, uniform limit for a parameter, but this isn't the usual case. On |
| most systems, it's possible for different file systems (and, for some |
| parameters, even different files) to have different maximum limits. For |
| example, this is very likely if you use NFS to mount some of the file |
| systems from other machines. |
| |
| <p><a name="index-limits_002eh-3647"></a>Each of the following macros is defined in <samp><span class="file">limits.h</span></samp> only if the |
| system has a fixed, uniform limit for the parameter in question. If the |
| system allows different file systems or files to have different limits, |
| then the macro is undefined; use <code>pathconf</code> or <code>fpathconf</code> to |
| find out the limit that applies to a particular file. See <a href="Pathconf.html#Pathconf">Pathconf</a>. |
| |
| <p>Each parameter also has another macro, with a name starting with |
| ‘<samp><span class="samp">_POSIX</span></samp>’, which gives the lowest value that the limit is allowed to |
| have on <em>any</em> POSIX system. See <a href="File-Minimums.html#File-Minimums">File Minimums</a>. |
| |
| <p><a name="index-limits_002c-link-count-of-files-3648"></a><!-- limits.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Macro: int <b>LINK_MAX</b><var><a name="index-LINK_005fMAX-3649"></a></var><br> |
| <blockquote><p>The uniform system limit (if any) for the number of names for a given |
| file. See <a href="Hard-Links.html#Hard-Links">Hard Links</a>. |
| </p></blockquote></div> |
| |
| <p><a name="index-limits_002c-terminal-input-queue-3650"></a><!-- limits.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Macro: int <b>MAX_CANON</b><var><a name="index-MAX_005fCANON-3651"></a></var><br> |
| <blockquote><p>The uniform system limit (if any) for the amount of text in a line of |
| input when input editing is enabled. See <a href="Canonical-or-Not.html#Canonical-or-Not">Canonical or Not</a>. |
| </p></blockquote></div> |
| |
| <!-- limits.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: int <b>MAX_INPUT</b><var><a name="index-MAX_005fINPUT-3652"></a></var><br> |
| <blockquote><p>The uniform system limit (if any) for the total number of characters |
| typed ahead as input. See <a href="I_002fO-Queues.html#I_002fO-Queues">I/O Queues</a>. |
| </p></blockquote></div> |
| |
| <p><a name="index-limits_002c-file-name-length-3653"></a><!-- limits.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Macro: int <b>NAME_MAX</b><var><a name="index-NAME_005fMAX-3654"></a></var><br> |
| <blockquote><p>The uniform system limit (if any) for the length of a file name component. |
| </p></blockquote></div> |
| |
| <!-- limits.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: int <b>PATH_MAX</b><var><a name="index-PATH_005fMAX-3655"></a></var><br> |
| <blockquote><p>The uniform system limit (if any) for the length of an entire file name (that |
| is, the argument given to system calls such as <code>open</code>). |
| </p></blockquote></div> |
| |
| <p><a name="index-limits_002c-pipe-buffer-size-3656"></a><!-- limits.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Macro: int <b>PIPE_BUF</b><var><a name="index-PIPE_005fBUF-3657"></a></var><br> |
| <blockquote><p>The uniform system limit (if any) for the number of bytes that can be |
| written atomically to a pipe. If multiple processes are writing to the |
| same pipe simultaneously, output from different processes might be |
| interleaved in chunks of this size. See <a href="Pipes-and-FIFOs.html#Pipes-and-FIFOs">Pipes and FIFOs</a>. |
| </p></blockquote></div> |
| |
| <p>These are alternative macro names for some of the same information. |
| |
| <!-- dirent.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: int <b>MAXNAMLEN</b><var><a name="index-MAXNAMLEN-3658"></a></var><br> |
| <blockquote><p>This is the BSD name for <code>NAME_MAX</code>. It is defined in |
| <samp><span class="file">dirent.h</span></samp>. |
| </p></blockquote></div> |
| |
| <!-- stdio.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>FILENAME_MAX</b><var><a name="index-FILENAME_005fMAX-3659"></a></var><br> |
| <blockquote><p>The value of this macro is an integer constant expression that |
| represents the maximum length of a file name string. It is defined in |
| <samp><span class="file">stdio.h</span></samp>. |
| |
| <p>Unlike <code>PATH_MAX</code>, this macro is defined even if there is no actual |
| limit imposed. In such a case, its value is typically a very large |
| number. <strong>This is always the case on the GNU system.</strong> |
| |
| <p><strong>Usage Note:</strong> Don't use <code>FILENAME_MAX</code> as the size of an |
| array in which to store a file name! You can't possibly make an array |
| that big! Use dynamic allocation (see <a href="Memory-Allocation.html#Memory-Allocation">Memory Allocation</a>) instead. |
| </p></blockquote></div> |
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