Why does StartsWith return the wrong value only on my machine?

user_11220 0
Viewed 227

The following code works on "everyones" machine, except for mine:

var foo = "caa";
var bar = "ca";
if (foo.StartsWith(bar, false, CultureInfo.GetCultureInfo("no")))
    Console.WriteLine($"{foo} starts with {bar}");
else
{
    Console.WriteLine($"{foo} does not start with {bar}");
}

I've tried in on .net 5.0.400, 5.0.403, 6.0.100 - all prints 'caa does not start with ca'. I've not copied the chars from anywhere, I literally type them out.

I understand that this is really just on my computer, but I do not understand why or what is causing this.

Edit: I'm on Windows 10 - OS Build: 19043.1348. nb-NO keyboard, en-US Windows UI language.

Edit: Added if (foo.StartsWith(bar, false, CultureInfo.GetCultureInfo("no") - no change in behavior.

.net c#
1 Answers

Repro:

System.Threading.Thread.CurrentThread.CurrentCulture = new CultureInfo("nb-NO");

var foo = "caa";
var bar = "ca";
if (foo.StartsWith(bar))
{
    Console.WriteLine($"{foo} starts with {bar}");
}
else
{
    Console.WriteLine($"{foo} does not start with {bar}");
}

Since .NET 5, string comparison is done using different string comparison libraries (ICU). In Norwegian, "aa" apparently isn't the same as "a" + "a". See Behavior changes when comparing strings on .NET 5+.

Compare (thanks @Charlieface):

You'll want an ordinal (character numeric value) comparison:

foo.StartsWith(bar, StringComparison.Ordinal)
user_2661430
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