php strpos总是返回false，我想得到一个正确的答案

I get a project and i see a piece of code as follows:

<?php
$orderby=$_REQUEST['orderby'];
if(strpos($orderby,'d')===true){
    echo "exists";
}else{
    echo "not ";
}?>

In any case , i input 'd' or others parameters the page always returning 'not'. so, how to input correct parameter make the page returning 'exists'?

strpos() can never return TRUE. If the string is found it returns the position. If the string is not found it returns FALSE. So you should compare with FALSE, not TRUE.

if (strpos($orderby, 'd') === false) {
    echo "not exists";
} else {
    echo "exists";
}

Your test is not saying that it is returning false, just that strpos() never returns a value of a boolean true. Instead it will return an integer with the position of the string found. Normally the check would be

if(strpos($orderby,'d') !== false){
    echo "exists";
}else{
    echo "not ";
}

if strpos finds a match, it won't give back true but the offset - so your strpos($orderby,'d')===true is never hit.

Try this:

<?php
$orderby=$_REQUEST['orderby'];
if($o=strpos($orderby,'d')===false){
    echo "not ";
}else{
    echo "exists at offset $o";
}?>