A fairly common problem you will run into is requiring the replacement of a string with something else.

Take, for example, the common issue where you need to represent the name ng'ang'a in a SQL statement.

Update Customers set Name = 'Ng'ang'a' where ID = 1

You can see here that the query breaks because the parser thinks the string ends at ng.

You solve this problem by escaping the single quote, ' with a second.

Update Customers set Name = 'Ng''ang''a where ID = 1

This is achieved in code as follows:

var sql = "Update Customers set Name = 'Ng'ang'a where ID = 1".Replace("'","''")

Suppose we wanted to make multiple such substitutions.

Typically we’d chain the replacements as follows:

var sql = "Update Customers set Name = 'Ng'ang'a where ID = 1"
		.Replace("'", "''")
		.Replace("\"", "\"\"")

Which works.

The problem with this is as you add more substitutions, the code becomes slower and slower as the runtime will need to generate a lot of intermediate strings for each of these replacements.

If they are very many, and the string is large, the performance will get worse and worse.

Take, for example, a case where I need to prefix each of these with a slash \ for some processing.

Writing this using string replacement would yield the following:

string[] specialCharacters =
    ["\\", "+", "-", "!", "(", ")", "{", "}", "[", "]", "^", "\"", "~", "*", "?", ":", "/", "'"];

// Escape all special characters
foreach (var specialCharacter in specialCharacters)
    searchCriteria = searchCriteria.Replace(specialCharacter, $@"\{specialCharacter}");

This can be written using a regular expression as follows:

var sql = "Update Customers set Name = 'Ng'ang'a where ID = 1";
sql = Regex.Replace(sql, @"[\\+\-!(){}\[\]^""~*?:/']", @"\$0");

Here we are doing the following:

  1. We are passing our pattern as a search expression of alternate characters - [\\+\-!(){}\[\]^""~*?:/']
  2. We are using the Replace method of the Regex to perform the substitution.

It works just as well as the former approach, and ought to perform pretty well as additional characters are added, or with large strings.

TLDR

Rather than using string.Replace in a loop, you can use the Regex.Replace method to replace multiple characters in a string.

Happy hacking!