replace the 2nd match skipping 1st match in C# [closed]

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i have a string which has 2 similar words..i want to replace the 2 secon开发者_C百科d word but not the 1st one..any help??

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You could use regular expressions and a lookbehind.

var replaceHello = "ABC hello 123 hello 456 hello 789";
var fixedUp = Regex.Replace(replaceHello, "(?<=hello.*)hello", "goodbye"); 

This will replace all instances of the word "hello" with "goodbye", except for the first.

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The Regex version is concise, but if you're not of the sort to use a regular expression, you could consider something more code heavy.

The StringBuilder class provides a way to replace within a given substring. In this extension method on string, we'll specify a substring that starts at the conclusion of the first applicable match. Some basic validation against arguments are in place, but I can't say I've tested all combinations.

public static string SkipReplace(this string input, string oldValue, string newValue)
{
    if (input == null)
        throw new ArgumentNullException("input");

    if (string.IsNullOrEmpty(oldValue))
        throw new ArgumentException("oldValue");

    if (newValue == null)
        throw new ArgumentNullException("newValue");

    int index = input.IndexOf(oldValue);

    if (index > -1)
    {
        int startingPoint = index + oldValue.Length;
        int count = input.Length - startingPoint;
        StringBuilder builder = new StringBuilder(input);
        builder.Replace(oldValue, newValue, startingPoint, count);

        return builder.ToString();
    }

    return input;
}

Using it:

string foobar = "foofoo".SkipReplace("foo", "bar");