Problem using NSString compare:options:range, conflicting results

Question

Ohh, what is wrong with this code !?!?!

    NSString *s1 = @"5 Oct 2010 18:30";
    NSString *s2 = @"5 Oct 2010 09:47";
    NSRange range = {0, 11}; // Both "D MMM YYYY " and "DD MMM YYYY"
    NSComparisonResult result = 0;
    result = [s1 compare:s2 options:NSLiteralSearch range:range];
    // result == -1
    NSString *sa = [s1 substringWithRange:range];
    NSString *sb = [s2 substringWithRange:range];
    result = [sa compare:sb];
    // result == 0

Why do I get different results from those two comperes? As far as I can tell, they should be same?

Answer 1

There's nothing wrong with it; sa and sb have the same values, but s1 and s2 do not.

EDIT:

Sorry, read it too quickly. There is indeed a problem - see below.

Answer 2

Here's a better answer, thanks to the kind people at the CocoaDev mailing list!

The 'range' referred to in the method signature is the range of the receiving string only.

So, in your first example, you are comparing the characters in range of s1 with the whole of s2; and that, correctly, is reported as -1.

This explains the apparent anomaly noted by fluchtpunkt, as well.