Regex vs Tryparse what is the best in performance

Question

In my ASP.net project I need to validate some basic data types for user inputs. The data types are like numeric, decimal, datetime etc.

What is the best approach that I should have taken in terms of performance? Is it to do it by Regex.IsMatch() or by TryParse()?

Thanks in advance.

Answer 1

TryParse and Regex.IsMatch are used for two fundamentally different things. Regex.IsMatch tells you if the string in question matches some particular pattern. It returns a yes/no answer. TryParse actually converts the value if possible, and tells you whether it succeeded.

Unless you're very careful in crafting the regular expression, Regex.IsMatch can return true when TryParse will return false. For example, consider the simple case of parsing a byte. With TryParse you have:

byte b;
bool isGood = byte.TryParse(myString, out b);

If the value in myString is between 0 and 255, TryParse will return true.

Now, let's try with Regex.IsMatch. Let's see, what should that regular expression be? We can't just say @"\d+" or even @\d{1,3}". Specifying the format becomes a very difficult job. You have to handle leading 0s, leading and trailing white space, and allow 255 but not 256.

And that's just for parsing a 3-digit number. The rules get even more complicated when you're parsing an int or long.

Regular expressions are great for determining form. They suck when it comes to determining value. Since our standard data types all have limits, determining its value is part of figuring out whether or not the number is valid.

You're better off using TryParse whenever possible, if only to save yourself the headache of trying to come up with a reliable regular expression that will do the validation. It's likely (I'd say almost certain) that a particular TryParse for any of the native types will execute faster than the equivalent regular expression.

The above said, I've probably spent more time on this answer than your Web page will spend executing your TryParse or Regex.IsMatch--total throughout its entire life. The time to execute these things is so small in the context of everything else your Web site is doing, any time you spend pondering the problem is wasted.

Use TryParse if you can, because it's easier. Otherwise use Regex.