php 5 strpos() difference between returning 0 and false?

Question

if(strpos("http://www.example.com","http://www.")==0){ // do work} 

I'd expect this to resolve as true, which it does. But what happens when I do

if(strpos("abcdefghijklmnop","http://www.")==0){// do work} 

This also passes on php 5 because as far as I can work out the strpos returns false which translates as 0.

Is this correct thinking/behaviour? If so what is the workaround for testing for that a substring is at the beginning of another string?

Answer 1

Yes, this is correct / expected behavior :

• strpos can return 0 when there is a match at the beginning of the string
• and it will return false when there is no match

The thing is you should not use == to compare 0 and false ; you should use ===, like this :

if(strpos("abcdefghijklmnop","http://www.") === 0) {  } 

Or :

if(strpos("abcdefghijklmnop","http://www.") === false) {  } 

For more informations, see Comparison Operators :

• $a == $b will be TRUE if $a is equal to $b.
• $a === $b will be TRUE if $a is equal to $b, and they are of the same type.

And, quoting the manual page of strpos :

This function may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE, such as 0 or "".
Please read the section on Booleans for more information.
Use the === operator for testing the return value of this function.