String literals in the PHP script are encoded with the same encoding that the PHP file was saved with. This is not affected by default_charset or other .ini settings.
Scenario: The default_charset is KOI8-R, and there is a text file "input.txt" containing the string "Это текст для поиска." in KOI8-R encoding.
A PHP script is written:
<?php
$string = 'текст.';
$data = file_get_contents('input.txt');
echo mb_strpos($data, $string);
?>
But unfortunately it was saved as UTF-8.
It doesn't work; mb_strpos() returns false because it can't find the UTF-8-encoded "текст" inside the KOI8-R-encoded "Это текст для поиска.".
Adjusting the default_charset had no effect. Not even fiddling with mb_internal_encoding could fix it, simply because the strings involved had *different* encodings and without actually changing one of them they just weren't going to match.
Either re-save the source file as KOI8-R to match the data file, or re-save the data file as UTF-8 to match the source code. Only then will the script properly echo '4'.
