Can't compare strings by alphabetical order-CodePudding

My DB stores keys by alphabetical order:

-MmNI8oyb2QE_9V0WdaX \\1st (oldest)
-MmOAFDL9ZPD1gx4SjEU \\2nd
-MmPtIJ1LpFTRbweNWvD \\3rd
-MmPtd0IMuNIEYaPYPgZ \\4th (newest)

The sorting order on this list is correct you can check here that it's an alphabetical order. 1st string is the smallest, then 2nd, 3rd, and 4th.

I would like to compare every two strings from that list, and get the correct results like the order of that specific list, so if I compare the 4th string with the 3rd one, I'll receive a result that 4th is bigger than the 3rd.

What I tried so far: using string.Compare, however it doesn't work right for my specific list the results I received weren't consistent

string first="-MmNI8oyb2QE_9V0WdaX";
string second="-MmOAFDL9ZPD1gx4SjEU";
string third="-MmPtIJ1LpFTRbweNWvD";
string fourth="-MmPtd0IMuNIEYaPYPgZ";
string.Compare(third,fourth) //output: 1
string.Compare(second,third) //output: -1
string.Compare(first,second) //output: -1

(Output should all be either "1" or "-1". because my list is sorted) What function should I use instead of comparing the strings? I also tried string.Compare(3rd,4th,false) an overload which compares by the case but it didn't help, my guess is that it has to do something with the case

CodePudding user response：

It seems you actually want to sort these strings by their ordinal value (their binary representation). In that case use StringComparison.Ordinal as comparisonType.

 string.Compare(third, fourth, StringComparison.Ordinal)); //output: -27
 string.Compare(second, third, StringComparison.Ordinal)); //output: -1
 string.Compare(first, second, StringComparison.Ordinal)); //output: -1

Weirdly the first comparison yields -27 instead of -1. The Compare method only specifies that the return value will be <1, 0 or >1 so those three output are essentially (and semantically) the same result.

CodePudding user response：

This is an interesting phenomenon that is likely caused by .NET performing a word-sort comparison, using weighted sorting rules to keep similar words together (see remarks here).

It causes some interesting, if unexpected, results. Even when case-sensitivity is false:

string.Compare("A", "c", false); // -1
string.Compare("a", "c", false); // -1
string.Compare("E", "c", false); // 1
string.Compare("e", "c", false); // 1

For strict comparison that uses the character code ordering, you want to use an Ordinal comparison method.

// UPPERCASE letters come before lowercase.
string.Compare("A", "c", StringComparison.Ordinal); // -34
string.Compare("a", "c", StringComparison.Ordinal); // -2
string.Compare("E", "c", StringComparison.Ordinal); // -30
string.Compare("e", "c", StringComparison.Ordinal); // 2