substr_replace encoding in PHP -

i want write text file. when use substr_replace in php encoding changes. doesn't print greek characters correctly. if don't fine. suggestions?

<?php $file = "test.txt"; $writefile = fopen($file, "w+");//read/write $myarray = array("δφδφ","δφδσφδσ","δφδφδ"); $myarray[0] = substr_replace($myarray[0],"ε", 0,1);  foreach ($myarray $data){       fwrite($writefile, $data."\n"); } ?> 

outcome
ε�φδφ
δφδσφδσ
δφδφδ

outcome no substr_replace
δφδφ
δφδσφδσ
δφδφδ

assuming you're encoding greek in multi-byte encoding (like utf-8), won't work because core php string functions, including substr_replace, not multi-byte aware. treat 1 character equal 1 byte, means you'll end slicing multi-byte characters in half if replace first byte. need use more manual approach involving multi-byte aware string function mb_substr:

mb_internal_encoding('utf-8'); echo 'ε' . mb_substr('δφδφ', 1); 

the comment @arma links to in comments wraps functionality in function.