Why does CompareTo not sort my string using ASCII code ordering?

Question

In C# "123-delete.json".CompareTo("123.json") evaluates to 1, meaning "123-delete.json" is to be sorted after "123.json".

This is unexpected for me, as according to the ASCII table . comes after -.

I tried to browse the CompareTo implementation on GitHub, but it seems this logic is implemented in a native function (InternalCompareString).

Why does the CompareTo method not follow the ASCII ordering?

Also, is there a way to view the source code for native functions such as InternalCompareString?

Answer 1

Use

string.Compare("123-delete.json", "123.json", StringComparison.Ordinal)

or

string.CompareOrdinal("123-delete.json", "123.json")

or

StringComparer.Ordinal.Compare("123-delete.json", "123.json")

In C# the comparison of strings is by default culture dependent and StringComparison.Ordinal lets the function compre the strings based on binary sort rules.

As @JeppeStigNielsen mentioned, the object returned by StringComparer.Ordinal implements the IComparer<string> interface, this lets you use this kind of sorting order in scenarios where you have a SortedSet<string>, SortedList<string> or any kind of "set" of strings that make use of an compare-object.