devdocs/elisp/substitution.html


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 <h3 class="section">Substituting for a Character Code</h3>   <p>The following functions replace characters within a specified region based on their character codes. </p> <dl> <dt id="subst-char-in-region">Function: <strong>subst-char-in-region</strong> <em>start end old-char new-char &amp;optional noundo</em>
</dt> <dd>
 <p>This function replaces all occurrences of the character <var>old-char</var> with the character <var>new-char</var> in the region of the current buffer defined by <var>start</var> and <var>end</var>. Both characters must have the same length of their multibyte form. </p>  <p>If <var>noundo</var> is non-<code>nil</code>, then <code>subst-char-in-region</code> does not record the change for undo and does not mark the buffer as modified. This was useful for controlling the old selective display feature (see <a href="selective-display">Selective Display</a>). </p> <p><code>subst-char-in-region</code> does not move point and returns <code>nil</code>. </p> <div class="example"> <pre class="example">---------- Buffer: foo ----------
This is the contents of the buffer before.
---------- Buffer: foo ----------
</pre>

<pre class="example">(subst-char-in-region 1 20 ?i ?X)
     ⇒ nil

---------- Buffer: foo ----------
ThXs Xs the contents of the buffer before.
---------- Buffer: foo ----------
</pre>
</div> </dd>
</dl> <dl> <dt id="subst-char-in-string">Function: <strong>subst-char-in-string</strong> <em>fromchar tochar string &amp;optional inplace</em>
</dt> <dd>
 <p>This function replaces all occurrences of the character <var>fromchar</var> with <var>tochar</var> in <var>string</var>. By default, substitution occurs in a copy of <var>string</var>, but if the optional argument <var>inplace</var> is non-<code>nil</code>, the function modifies the <var>string</var> itself. In any case, the function returns the resulting string. </p>
</dd>
</dl> <dl> <dt id="translate-region">Command: <strong>translate-region</strong> <em>start end table</em>
</dt> <dd>
<p>This function applies a translation table to the characters in the buffer between positions <var>start</var> and <var>end</var>. </p> <p>The translation table <var>table</var> is a string or a char-table; <code>(aref <var>table</var> <var>ochar</var>)</code> gives the translated character corresponding to <var>ochar</var>. If <var>table</var> is a string, any characters with codes larger than the length of <var>table</var> are not altered by the translation. </p> <p>The return value of <code>translate-region</code> is the number of characters that were actually changed by the translation. This does not count characters that were mapped into themselves in the translation table. </p>
</dd>
</dl><div class="_attribution">
  <p class="_attribution-p">
    Copyright &copy; 1990-1996, 1998-2022 Free Software Foundation, Inc. <br>Licensed under the GNU GPL license.<br>
    <a href="https://www.gnu.org/software/emacs/manual/html_node/elisp/Substitution.html" class="_attribution-link">https://www.gnu.org/software/emacs/manual/html_node/elisp/Substitution.html</a>
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