字符串中的String.Empty

Question

2 days ago, there was a question related to string.LastIndexOf(String.Empty) returning the last index of string:

Do C# strings end with empty string?

So I thought that; a string can always contain string.empty between characters like:

"testing" == "t" + String.Empty + "e" + String.Empty +"sting" + String.Empty;

After this, I wanted to test if String.IndexOf(String.Empty) was returning 0 because since String.Empty can be between any char in a string, that would be what I expect it to return and I wasn't wrong.

string testString = "testing";
int index = testString.LastIndexOf(string.Empty); // index is 6
index = testString.IndexOf(string.Empty); // index is 0

It actually returned 0. I started to think that if I could split a string with String.Empty , I would get at least 2 string and those would be String.Empty and rest of the string since String.IndexOf(String.Empty) returned 0 and String.LastIndexOf(String.Empty) returned length of the string.. Here is what I coded:

string emptyString = string.Empty;
char[] emptyStringCharArr = emptyString.ToCharArray();
string myDummyString = "abcdefg";
string[] result = myDummyString.Split(emptyStringCharArr);

The problem here is, I can't obviously convert String.Empty to char[] and result in an empty string[]. I would really love to see the result of this operation and the reason behind this. So my questions are:

1. Is there any way to split a string with String.Empty ?

2. If it is not possible but in an absolute world which it would be possible, would it return an array full of chars like [0] = "t" [1] = "e" [2] = "s" and so on or would it just return the complete string? Which would make more sense and why?

Answer 1

You will always get an Index of 0 when you look for String.Empty in any String, because it's the definition of String.IndexOf(String.Empty) you should have a look at the MSDN , where it says:

"The zero-based index position of value if that string is found, or -1 if it is not. If value is String.Empty, the return value is 0."

Directed to your second Question:

I think you can Split a String with an Empty String by doing something like this in your code:

String test = "fwewfeoj";
test.Split(new String[] { String.Empty }, StringSplitOptions.None);

By the way: Possible Clone of this answer Why does "abcd".StartsWith("") return true?

Answer 2

是的，您可以使用字符串.Empty拆分任何字符串

 string[] strArr = s.Split(string.Empty.ToCharArray());

Answer 3

Do you really need to split the string, or are you just trying to get all the individual characters?

If so, then a string is also a IEnumerable<char> , and you also have an indexer.

So, what are you actually trying to do?

And no, you can't call the split methods with string.Empty or similar constructs.

Answer 4

string emptyString = string.Empty;
char[] emptyStringCharArr = emptyString.ToCharArray();

This will give you an empty array of chars. This is because String is already an array of chars in memory, and String.Empty has no value.

To break it down further, consider an implementation of .ToCharArray()

private Char[] toCharArray(String value)
{
    var stringLength = value.Length;
    var returningArray = new char[stringLength];
    for(var i = 0; i < stringLength; i++)
    {
        returningArray[i] = value[i];
    }
    return returningArray;
}

Length of course will be zero, and you will return an empty char array. Of course this isn't the exact implementation, but you can see how and why it's returning nothing (and therefore isn't splitting on the string as you're expecting it to)

It's not an array with a single element String.Empty, because that doesn't really make sense. When you try to split on an empty array, it doesn't know how or what to split on, so you're given back the original string.

As for why it returns 0 by default, consider:

private int IndexOf(String value, String searchFor)
{
    for(var i = 0; i < value.Length; i++)
    {
        if(value.Substring(i, searchFor.Length) == searchFor)
        {
            return i;
        }
    }
    return -1;
}
private int LastIndexOf(String value, String searchFor)
{
    var searchLength = searchFor.Length;
    for(var i = value.Length - searchFor.Length; i >= 0; i--)
    {
        if(value.Substring(i, searchLength) == searchFor)
            return i;
    }
    return -1;
}

String.SubString(x, 0) will ALWAYS return String.Empty, regardless of what's passed in (even String.Empty). For this reason it's much faster to add a check and return 0 regardless (as it would even if it ran the loop).

Answer 5

Since String.Empty is just an empty string, so if you do:

var s = "part1" + string.Empty + "part2";

this will result in exactly the same string as:

var s = "part1" + "part2";

the first syntax will not insert a magic empty string between the two parts.

That IndexOf returns 0, is by definition, not because there is some magic empty string between characters.

I cannot think of a logic way to split a string, by an empty string. What should it return? When using an empty string as an argument to the string.Split method, it will be ignored. If it was the only separator to use, the string will be returned unsplit.

Answer 6

you could also say

"testing" == string.Empty + string.Empty + string.Empty + ... + "t" +  string.Empty + string.empty + "esting";

So actually you could place an endless array of string.empty between each character.

So I think 1 not possible 2 none, it just doens't make sense...