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mb_strrpos() returns the wrong position for a negative offset in a non-UTF-8 encoding #22779
Description
Description
The following code:
<?php
var_dump(mb_strrpos("\xA9\xA9X", "\xA9", -2, "ISO-8859-1"));
var_dump(strrpos("\xA9\xA9X", "\xA9", -2));Resulted in this output:
int(0)
int(1)
But I expected this output instead:
int(1)
int(1)
For a single-byte encoding one byte is one character, so mb_strrpos() should agree with strrpos() here. The result is wrong for a negative offset in any non-UTF-8 encoding. An ISO-8859-1 needle byte in 0x80-0xBF gives a position that is too early, and an ASCII needle in UTF-16 also returns the wrong position.
PHP Version
PHP 8.4.25-dev (the same code is in 8.3, 8.5 and master)
Operating System
macOS 27.0
Activity
youkidearitai commentedon Jul 17, 2026
Thanks for report. I confirmed behavior changes from PHP 8.3
https://3v4l.org/MpZOD#veol
@alexdowad What do you think?
alexdowad commentedon Jul 17, 2026
@youkidearitai I commented in @eyupcanakman's PR.
Fix GH-22779: mb_strrpos() wrong result in a non-UTF-8 encoding
bug #693 [Mbstring] Fix search functions that ignore the needle, offs…