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Clarify that mb_strpos returns a character position, not a byte position #5853

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Merged
lacatoire merged 2 commits into from
Sep 10, 2026
Merged

Clarify that mb_strpos returns a character position, not a byte position #5853

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d8cc9c8
Clarify mb_strpos returns character position, not byte; add example
lacatoire Sep 10, 2026
acb8311
Clarify offset parameter is in characters
lacatoire Sep 10, 2026
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45 changes: 36 additions & 9 deletions reference/mbstring/functions/mb-strpos.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -52,10 +52,10 @@
<varlistentry>
<term><parameter>offset</parameter></term>
<listitem>
<para>
The search offset. If it is not specified, 0 is used.
<simpara>
The search offset in characters. If it is not specified, 0 is used.
A negative offset counts from the end of the string.
</para>
</simpara>
</listitem>
</varlistentry>
<varlistentry>
Expand All @@ -70,12 +70,12 @@

<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
Returns the numeric position of
the first occurrence of <parameter>needle</parameter> in the
<parameter>haystack</parameter> <type>string</type>. If
<parameter>needle</parameter> is not found, it returns &false;.
</para>
<simpara>
Returns the character position (not byte position) of the first occurrence
of <parameter>needle</parameter> in the <parameter>haystack</parameter>
<type>string</type>, counting from <literal>0</literal>.
Returns &false; if <parameter>needle</parameter> is not found.
</simpara>
</refsect1>

<refsect1 role="errors">
Expand Down Expand Up @@ -115,10 +115,37 @@
</informaltable>
</refsect1>

<refsect1 role="examples">
&reftitle.examples;
<example>
<title><function>mb_strpos</function> returns a character offset, not a byte offset</title>
<programlisting role="php">
<![CDATA[
<?php
// "🐘" is 4 bytes but 1 character; "é" is 2 bytes but 1 character
$str = "🐘H🐘é";

var_dump(mb_strpos($str, "é")); // character 3, not byte 9
var_dump(mb_strpos($str, "🐘", 1)); // character 2, skipping the first "🐘"
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
int(3)
int(2)
]]>
</screen>
</example>
</refsect1>

<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>mb_strrpos</function></member>
<member><function>mb_stripos</function></member>
<member><function>mb_internal_encoding</function></member>
<member><function>strpos</function></member>
</simplelist>
Expand Down