Compare

The Compare method determines the sort order of strings. It checks if one string is ordered before another when in alphabetical order, whether it is ordered after, or is equivalent.

Method info

There are 3 methods that provide this functionality—Compare, CompareOrdinal and CompareTo. Two strings are always compared.

An example

We need the Compare methods for sorting algorithms. We use them to test whether one string comes before or after the other in sorting.

using System;

string a = "a";
string b = "b";

// Part 1: use static Compare.
int c = string.Compare(a, b);
Console.WriteLine(c);

// Part 2: use static CompareOrdinal.
c = string.CompareOrdinal(b, a);
Console.WriteLine(c);

// Part 3: use CompareTo.
c = a.CompareTo(b);
Console.WriteLine(c);

c = b.CompareTo(a);
Console.WriteLine(c);
-1       (This means a is smaller than b)
1        (This means b is smaller than a)
-1
1

Review, results

It is important to understand the possible results of Compare methods. Here are the int return values—we see just 3 values: -1, zero, and 1.

String A: First alphabetically
String B: Second alphabetically

Compare(A, B): -1
Compare(B, A):  1

Compare(A, A):  0
Compare(B, B):  0

Notes, globalization

By default, string.Compare and CompareTo use the system globalization for safe comparisons. Cultures such as Turkish have common letters that need globalization.

A discussion

All sorting algorithms must see if one string should be ordered before any other string. The Compare methods are ideal for when you need to implement your own sorting methods.

Case

String comparisons are by default case-sensitive. But you can use the StringComparison.OrdinalIgnoreCase enumerated constant to use a case-insensitive comparison.

A summary

The Compare methods see if one string is larger, smaller or equal to another. Compare returns 1, 0 or -1 if a string is alphabetically first, equal, or second.