iconv UTF-8//IGNORE still produces "illegal character" error

Question

$string = iconv("UTF-8", "UTF-8//IGNORE", $string);

I thought this code would remove invalid UTF-8 characters, but it produces [E_NOTICE] "iconv(): Detected an illegal character in input string". What am I missing, how do I properly strip a string from illegal characters?

Answer 1

The output character set (the second parameter) should be different from the input character set (first param). If they are the same, then if there are illegal UTF-8 characters in the string, iconv will reject them as being illegal according to the input character set.