string.insert multiple values. Is this possible?

问题:

Im still learning in C#, and there is one thing i cant really seem to find the answer to.

If i have a string that looks like this "abcdefg012345", and i want to make it look like "ab-cde-fg-012345"

i tought of something like this:

  string S1 = "abcdefg012345";
            string S2 = S1.Insert(2, "-");
            string S3 = S2.Insert(6, "-");
            string S4 = S3.Insert.....
                ...
                ..

Now i was looking if it would be possible to get this al into 1 line somehow, without having to make all those strings.

I assume this would be possible somehow ?

回答1:

Whether or not you can make this a one-liner (you can), it will always cause multiple strings to be created, due to the immutability of the String in .NET

If you want to do this somewhat efficiently, without creating multiple strings, you could use a StringBuilder. An extension method could also be useful to make it easier to use.

public static class StringExtensions
{
    public static string MultiInsert(this string str, string insertChar, params int[] positions)
    {
        StringBuilder sb = new StringBuilder(str.Length + (positions.Length*insertChar.Length));
        var posLookup = new HashSet<int>(positions);
        for(int i=0;i<str.Length;i++)
        {
            sb.Append(str[i]);
            if(posLookup.Contains(i))
                sb.Append(insertChar);

        }
        return sb.ToString();

    }
}

Note that this example initialises StringBuilder to the correct length up-front, therefore avoiding the need to grow the StringBuilder.

Usage: "abcdefg012345".MultiInsert("-",2,5); // yields "abc-def-g012345"

Live example: http://rextester.com/EZPQ89741

回答2:

string S1 = "abcdefg012345".Insert(2, "-").Insert(6, "-")..... ;

回答3:

If the positions for the inserted strings are constant you could consider using string.Format() method. For example:

string strTarget = String.Format("abc{0}def{0}g012345","-");

回答4:

string s = "abcdefg012345";
foreach (var index in [2, 6, ...]
{
    s = s.Insert(index, "-");
}

回答5:

I like this

    StringBuilder sb = new StringBuilder("abcdefg012345");
    sb.Insert(6, '-').Insert(2, '-').ToString();

回答6:

        String s1 = "abcdefg012345";
        String seperator = "-";
        s1 = s1.Insert(2, seperator).Insert(6, seperator).Insert(9, seperator);

Chaining them like that keeps your line count down. This works because the Insert method returns the string value of s1 with the parameters supplied, then the Insert function is being called on that returned string and so on.

Also it's worth noting that String is a special immutable class so each time you set a value to it, it is being recreated. Also worth noting that String is a special type that allows you to set it to a new instance with calling the constructor on it, the first line above will be under the hood calling the constructor with the text in the speech marks.

回答7:

Just for the sake of completion and to show the use of the lesser known Aggregate function, here's another one-liner:

string result = new[] { 2, 5, 8, 15 }.Aggregate("abcdefg012345", (s, i) => s.Insert(i, "-"));

result is ab-cd-ef-g01234-5. I wouldn't recommend this variant, though. It's way too hard to grasp on first sight.

Edit: this solution is not valid, anyway, as the "-" will be inserted at the index of the already modified string, not at the positions wrt to the original string. But then again, most of the answers here suffer from the same problem.

回答8:

You should use a StringBuilder in this case as Strings objects are immutable and your code would essentially create a completely new string for each one of those operations. http://msdn.microsoft.com/en-us/library/2839d5h5(v=vs.71).aspx

Some more information available here: http://www.dotnetperls.com/stringbuilder

Example:

namespace ConsoleApplication10
{
    class Program
    {
        static void Main(string[] args)
        {
            StringBuilder sb = new StringBuilder("abcdefg012345");
            sb.Insert(2, '-');
            sb.Insert(6, '-');

            Console.WriteLine(sb);
            Console.Read();
        }
    }
}

If you really want it on a single line you could simply do something like this:

StringBuilder sb = new StringBuilder("abcdefg012345").Insert(2, '-').Insert(6, '-');