string.Format, regex + curly braces (C#)

Question

Hi all.

How do I use string.Format to enter a value into a regular expression, where that regular expression has curly-braces in it already to define repetition limitation? (My mind is cloudy from the collision for syntax)

e.g. The normal regex is "^\d{0,2}", and I wish to insert the '2' from the property MaxLength

Thanks.

Answer 1

You can escape curly braces by doubling them :

string.Format("Hello {{World}}") // returns "Hello {World}"

In your case, it would be something like that :

string regexPattern = string.Format("^\d{{0,{0}}}", MaxLength);

Answer 2

Replace single curly braces with double curly braces:

string regex = string.Format(@"^\d{{0,{0}}}", MaxLength);

If that makes your eyes hurt you could just use ordinary string concatenation instead:

string regex = @"^\d{0," + MaxLength + "}";

Answer 3

For details on the formatting strings, see MSDN

var regex = String.Format(@"^\d{{0,{0}{1}", this.MaxLength, "}")

And yes, the extra parameter is may be required (no, it's not in this case) due to the eccentricities of the way the braces are interpreted. See the MSDN link for more.

All in all, I have to agree with Mark, just go with normal string concatenation in this case.