find whether a string is a regular expression or normal string in C#

Question

How to find whether a string is a regular expression or normal string in C#. I find in java and PHP but not C#. Can anyone help me please. String testing = "Final";

I want to test whether "testing" is a regular expression or normal string.

Thankyou

What do you mean? Most normal strings can also be used as regular expressions. — Cristian Lupascu, Sep 27 '16 at 07:20
Indeed... I'm confused as to what you'd do in the other languages, too. Not all strings are valid regular expressions of course, but all regular expressions are also normal strings. — Jon Skeet, Sep 27 '16 at 07:22
@Madhu: Right, that's a normal string as well as a valid regular expression. — Jon Skeet, Sep 27 '16 at 07:22
string testing1 = "Final". Here testing contains regular expression. where as testing1 contains just a normal string. — Madhu, Sep 27 '16 at 07:22
check here http://stackoverflow.com/questions/172303/is-there-a-regular-expression-to-detect-a-valid-regular-expression — dumb_terminal, Sep 27 '16 at 07:23
I mean i just want to find whether has any expressions or not — Madhu, Sep 27 '16 at 07:24
yes i just want to filter all the strings that has expressions in it — Madhu, Sep 27 '16 at 07:25
`"Final"` is a correct regular expression. `"^[^a]*$"` is a valid "normal string" if someone wanted to get fancy. You can get close but you'd have to decide what _counts_ as a regular expression yourself. What methods do you use in Java/PHP? Perhaps their docs explain what validation rules they use. — C.Evenhuis, Sep 27 '16 at 07:31
yes tried with new Regex(testing); With always gives true because testing and testing1 both are valid regular expressions as said by Jon — Madhu, Sep 27 '16 at 07:36

score 2 · Answer 1 · answered Sep 27 '16 at 07:23

2

you can try by exception handling

private static bool IsValidRegex(string input)
{ 
   try
   {
     Regex.Match("", input);
   }
   catch (ArgumentException)
   {
      return false;
   }

  return true;
}

answered Sep 27 '16 at 07:23

Visakh V A

331
3
19

score 1 · Answer 2 · answered Sep 27 '16 at 07:24

1

You can evaulate string in Regex

private static bool IsValidRegex(string pattern)
{
    if (string.IsNullOrEmpty(pattern)) return false;

    try {
        Regex.Match("", pattern);
    }
    catch (ArgumentException){
        return false;
    }

    return true;
}

If method returns false you can accept this string as normal string.

answered Sep 27 '16 at 07:24

Dakmaz

61
6

Seems quite hacky to me to rely on exceptions, However I dount there is a nicer approach. – MakePeaceGreatAgain Sep 27 '16 at 07:26
@HimBromBeere I think there could be one which is inline function but you would need to create it in every request :( So, this is good enough ;) – Dakmaz Mar 20 '17 at 09:18

find whether a string is a regular expression or normal string in C#

2 Answers2