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

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.

CodePudding user response：

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 .

Edit: not sure why I included the tidbit above, AFAIK this did behave the same on earlier framework versions. Researching...

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

foo.StartsWith(bar, StringComparison.Ordinal)