Is String.Contains() faster than String.IndexOf()?

Contains(s2) is many times (in my computer 10 times) faster than IndexOf(s2) because Contains uses StringComparison.Ordinal that is faster than the culture sensitive search that IndexOf does by default (but that may change in .net 4.0 http://davesbox.com/archive/2008/11/12/breaking-changes-to-the-string-class.aspx).

Contains has exactly the same performance as IndexOf(s2,StringComparison.Ordinal) >= 0 in my tests but it's shorter and makes your intent clear.

I am running a real case (in opposite to a synthetic benchmark)

 if("=,<=,=>,<>,<,>,!=,==,".IndexOf(tmps)>=0) {

versus

 if("=,<=,=>,<>,<,>,!=,==,".Contains(tmps)) {

It is a vital part of my system and it is executed 131,953 times (thanks DotTrace).

However shocking surprise, the result is the opposite that expected

• IndexOf 533ms.
• Contains 266ms.

:-/

net framework 4.0 (updated as for 13-02-2012)

Contains calls IndexOf:

public bool Contains(string value)
{
    return (this.IndexOf(value, StringComparison.Ordinal) >= 0);
}

Which calls CompareInfo.IndexOf, which ultimately uses a CLR implementation.

If you want to see how strings are compared in the CLR this will show you (look for CaseInsensitiveCompHelper).

IndexOf(string) has no options and Contains()uses an Ordinal compare (a byte-by-byte comparison rather than trying to perform a smart compare, for example, e with é).

So IndexOf will be marginally faster (in theory) as IndexOf goes straight to a string search using FindNLSString from kernel32.dll (the power of reflector!).

Updated for .NET 4.0 - IndexOf no longer uses Ordinal Comparison and so Contains can be faster. See comment below.