If iconv_strlen is passed a UTF-8 string containing badly formed sequences, it will return FALSE. This is in contrast to mb_strlen of the behaviour of utf8_decode, which strip out any bad sequences;<?php# UTF-8 string containing bad sequence: \xe9$str = "I?t?rn?ti?n\xe9?liz?ti?n";print "mb_strlen: ".mb_strlen($str,'UTF-8')."\n";print "strlen/utf8_decode: ".strlen(utf8_decode($str))."\n";print "iconv_strlen: ".iconv_strlen($str,'UTF-8')."\n";?>Displays;mb_strlen: 20strlen/utf8_decode: 20iconv_strlen:(PHP 5.0.5)As such it is being "stricter" than mb_strlen and it may mean you need to check for invalid sequences first. A quick way to check is to exploit the behaviour of the PCRE extension (see notes on pattern modifiers);<?phpif (preg_match('/^.{1}/us',$str,$ar) != 1) { die("string contains invalid UTF-8");}?>A slower but stricter check (regex) can be found at: http://www.w3.org/International/questions/qa-forms-utf-8Similiar applies to iconv_substr, iconv_strpos and iconv_strrpos