Bug in C# - "FooBar".StartsWith(string.Empty) is true

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?

Check out http://stackoverflow.com/questions/145509/why-does-abcd-startswith-return-true/145516#145516 — Bala R, Mar 07 '11 at 14:36

score 4 · Accepted Answer · answered Mar 07 '11 at 14:36

4

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.

answered Mar 07 '11 at 14:36

一二三

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score 0 · Answer 2 · answered Mar 07 '11 at 14:34

0

Why do you think "this == value" evaluate to true? I believe this behavior is correct. Any string may be considered to be starting with empty string.

answered Mar 07 '11 at 14:34

Snowbear

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score 0 · Answer 3 · answered Mar 07 '11 at 14:36

0

Actually FooBar starts with string.Empty. Any string can be considered starting with string.Empty, as well as 0+a = a.

answered Mar 07 '11 at 14:36

Felice Pollano

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Bug in C# - "FooBar".StartsWith(string.Empty) is true

3 Answers3