objective c - string has prefix PHP

How make an if-statement that if $mystring has the prefix "http://" then {do something}.

I've done this in objective-c like this:

if([mynsstring hasPrefix:@"http://"])

{
//Do something...
}

I don't know how to do this in PHP.
Thanks for your help in advance.

Answer

Simplest would be using substring to compare

if (substr($mystring, 0, 7) === 'http://') {
     // do something
}

Remember of course to take the exact number of characters.