String.CompareTo with case

Question

Sample code to illustrate:

    int res1 = "a".CompareTo("A");  // res1 = -1
    int res2 = "ab".CompareTo("A");  // res2 = 1

I'm seeing res1 = -1, and res2 = 1 at the end, which was a bit unexpected. I thought res1 would return 1, since on an ASCII chart "A" (0x41) comes before "a" (0x61).

Also, it seems strange that for res2, the length of the string seems to make a difference. i.e. if "a" comes before "A" (as res1 = -1 indicates), then I would have thought that "a"withAnythingAfterIt would also come before "A"withAnythingAfterIt.

Can someone shed some light? Thanks.

Answer 1

This is the expected behavior. String.CompareTo(string) does a culture sensitive comparison, using its sort order. In fact it calls CultureInfo to do the job as we can see in the source code:

public int CompareTo(String strB) {
    if (strB==null) {
        return 1;
    }

    return CultureInfo.CurrentCulture.CompareInfo.Compare(this, strB, 0);
}

Your current culture puts 'A' after 'a' in the sort order, since it would be a tie, but not after 'ab' since clearly 'ab' comes after either 'a' or 'A' in most sort orders I know. It's just the tie breaking mechanism doing its work: when the sort order would be the same, use the ordinal value!