Question

Possible Duplicate:
Why does “abcd”.StartsWith(“”) return true?

Something similar to this being true caught us out:

"FooBar".StartsWith(string.Empty)

Firstly I don’t think it should be true but I am also not quite sure why it is true, looking at the “Reflector’ed” code:

public bool StartsWith(string value, bool ignoreCase, CultureInfo culture)
{
    if (value == null)
    {
        throw new ArgumentNullException("value");
    }
    if (this == value)
    {
        return true;
    }
    CultureInfo info = (culture == null) ? CultureInfo.CurrentCulture : culture;
    return info.CompareInfo.IsPrefix(this, value, ignoreCase ? CompareOptions.IgnoreCase : CompareOptions.None);
}

ignoreCase is false and culture is null. So why does “this == value” evaluate to true?

Answer 1

It’s not that this == value returns true, but CompareInfo.IsPrefix is documented as returning true for String.Empty:

Every string starts and ends with an
empty substring (“”); therefore, if
prefix is an empty string, this method
returns true.