CODEWITHSUNDEEP
c#regexstring
Vini
Vini

Reputation: 2134

Replacing the value of a substring but one

I need to replace all the occurrences of a sub-string with another string. But I do not want to replace the occurrence of a sub-string in a particular sub-string within the main string.

Example

string main = "The value for v and p are not v and p"
string replacestring= "v";
main = main.Replace(replacestring,12);

Result 

main = The 12alue for 12 and p are not 12 and p

Expected Result

main =The value for 12 and p are not v and p.

So basically I am not trying to skip the first occurrence of the substring but the whole sub-string value. I do not want it to be replaced for any value of replacestring. I have tried to find the index of the first occurrence of the sub-string value and skipping the next 4 characters and then replacing. But it isn't efficient enough for me as can have more than one occurrence of value.

Upvotes: 1

Views: 158

Answers (1)

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 627082

If you want to replace the first v as a whole word, use

var rx1 = new Regex(@"\bv\b");
var t = rx1.Replace("The value for v and p are not v and p", "12", 1);

enter image description here

See Regex.Replace method. The last 1 argument is count (the maximum number of times the replacement can occur.)

The regex \bv\b matches any v that is enclosed with non-word characters (non-letters, non-digits, and non-_s).

Whenever you are building a regex dynamically, make sure you

  • use verbatim string literals so as to use only single backslash to escape regex metacharacters
  • Regex.Escape method should be used when you need to match some value literally.

Thus, use

var s = "v";
var rx1 = new Regex(@"\b" + Regex.Escape(s) + @"\b");
// or
// var rx1 = new Regex(string.Format(@"\b{0}\b", Regex.Escape(s)));
var t = rx1.Replace("The value for v and p are not v and p", "12", 1);

Upvotes: 4

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