Check whether returned file is XML or not

Question

I need to check the return value of a website output. In case of valid login details it returns a XML file and in case of invalid login details it just returns a string sayi

Answer 1

Check if the first 5 characters equal <?xml, that should be a pretty good clue.

if(substr($output, 0, 5) == "<?xml") {
    echo 'Is XML';
} else {
    echo 'Not XML';
}

Answer 2

$result = simplexml_load_string ($data, 'SimpleXmlElement', LIBXML_NOERROR+LIBXML_ERR_FATAL+LIBXML_ERR_NONE);
if (false == $result) echo 'error';

Answer 3

Could also be because the first line of the return data is blank - try $output = trim($output) before you parse the string as XML.