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| Previous: <a rel="previous" accesskey="p" href="Subexpression-Complications.html#Subexpression-Complications">Subexpression Complications</a>, |
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| <h4 class="subsection">10.3.6 POSIX Regexp Matching Cleanup</h4> |
| |
| <p>When you are finished using a compiled regular expression, you can |
| free the storage it uses by calling <code>regfree</code>. |
| |
| <!-- regex.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Function: void <b>regfree</b> (<var>regex_t *compiled</var>)<var><a name="index-regfree-882"></a></var><br> |
| <blockquote><p>Calling <code>regfree</code> frees all the storage that <code>*</code><var>compiled</var> |
| points to. This includes various internal fields of the <code>regex_t</code> |
| structure that aren't documented in this manual. |
| |
| <p><code>regfree</code> does not free the object <code>*</code><var>compiled</var> itself. |
| </p></blockquote></div> |
| |
| <p>You should always free the space in a <code>regex_t</code> structure with |
| <code>regfree</code> before using the structure to compile another regular |
| expression. |
| |
| <p>When <code>regcomp</code> or <code>regexec</code> reports an error, you can use |
| the function <code>regerror</code> to turn it into an error message string. |
| |
| <!-- regex.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Function: size_t <b>regerror</b> (<var>int errcode, const regex_t *restrict compiled, char *restrict buffer, size_t length</var>)<var><a name="index-regerror-883"></a></var><br> |
| <blockquote><p>This function produces an error message string for the error code |
| <var>errcode</var>, and stores the string in <var>length</var> bytes of memory |
| starting at <var>buffer</var>. For the <var>compiled</var> argument, supply the |
| same compiled regular expression structure that <code>regcomp</code> or |
| <code>regexec</code> was working with when it got the error. Alternatively, |
| you can supply <code>NULL</code> for <var>compiled</var>; you will still get a |
| meaningful error message, but it might not be as detailed. |
| |
| <p>If the error message can't fit in <var>length</var> bytes (including a |
| terminating null character), then <code>regerror</code> truncates it. |
| The string that <code>regerror</code> stores is always null-terminated |
| even if it has been truncated. |
| |
| <p>The return value of <code>regerror</code> is the minimum length needed to |
| store the entire error message. If this is less than <var>length</var>, then |
| the error message was not truncated, and you can use it. Otherwise, you |
| should call <code>regerror</code> again with a larger buffer. |
| |
| <p>Here is a function which uses <code>regerror</code>, but always dynamically |
| allocates a buffer for the error message: |
| |
| <pre class="smallexample"> char *get_regerror (int errcode, regex_t *compiled) |
| { |
| size_t length = regerror (errcode, compiled, NULL, 0); |
| char *buffer = xmalloc (length); |
| (void) regerror (errcode, compiled, buffer, length); |
| return buffer; |
| } |
| </pre> |
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