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| <h4 class="subsection">10.3.4 Match Results with Subexpressions</h4> |
| |
| <p>When <code>regexec</code> matches parenthetical subexpressions of |
| <var>pattern</var>, it records which parts of <var>string</var> they match. It |
| returns that information by storing the offsets into an array whose |
| elements are structures of type <code>regmatch_t</code>. The first element of |
| the array (index <code>0</code>) records the part of the string that matched |
| the entire regular expression. Each other element of the array records |
| the beginning and end of the part that matched a single parenthetical |
| subexpression. |
| |
| <!-- regex.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Data Type: <b>regmatch_t</b><var><a name="index-regmatch_005ft-880"></a></var><br> |
| <blockquote><p>This is the data type of the <var>matcharray</var> array that you pass to |
| <code>regexec</code>. It contains two structure fields, as follows: |
| |
| <dl> |
| <dt><code>rm_so</code><dd>The offset in <var>string</var> of the beginning of a substring. Add this |
| value to <var>string</var> to get the address of that part. |
| |
| <br><dt><code>rm_eo</code><dd>The offset in <var>string</var> of the end of the substring. |
| </dl> |
| </p></blockquote></div> |
| |
| <!-- regex.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Data Type: <b>regoff_t</b><var><a name="index-regoff_005ft-881"></a></var><br> |
| <blockquote><p><code>regoff_t</code> is an alias for another signed integer type. |
| The fields of <code>regmatch_t</code> have type <code>regoff_t</code>. |
| </p></blockquote></div> |
| |
| <p>The <code>regmatch_t</code> elements correspond to subexpressions |
| positionally; the first element (index <code>1</code>) records where the first |
| subexpression matched, the second element records the second |
| subexpression, and so on. The order of the subexpressions is the order |
| in which they begin. |
| |
| <p>When you call <code>regexec</code>, you specify how long the <var>matchptr</var> |
| array is, with the <var>nmatch</var> argument. This tells <code>regexec</code> how |
| many elements to store. If the actual regular expression has more than |
| <var>nmatch</var> subexpressions, then you won't get offset information about |
| the rest of them. But this doesn't alter whether the pattern matches a |
| particular string or not. |
| |
| <p>If you don't want <code>regexec</code> to return any information about where |
| the subexpressions matched, you can either supply <code>0</code> for |
| <var>nmatch</var>, or use the flag <code>REG_NOSUB</code> when you compile the |
| pattern with <code>regcomp</code>. |
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