RegEx to validate conditions within if ()

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Hi, We are working on a program where we need to validate string within if (string )
Such that string is always a condition which needs to be evaluate.

Example :

C#

1) if (" 5 > 4 && 8/2 >= 3" ) -- In programming world condition within if () is true.
2) if (" 5 > 4 && > 8/2 >= 3" ) -- In programming world condition within if () is false.

Any suggestion / recommendation how to validate such strings within if ( ) will be of great help.

Regards

Posted 15-Apr-15 7:31am

ankurparikh

Updated 15-Apr-15 7:42am

Maciej Los

v2

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Thomas Daniels 15-Apr-15 13:38pm

Your question is tagged both C# and Java; which language do you use?

Matt T Heffron 15-Apr-15 13:50pm

Are you asking for a RegEx that will evaluate the condition? Or merely to indicate if it is "well formed"?
What are the constraints on the form of the conditions?
Both And and Or? Nested (in parentheses)?
This is almost certainly beyond a RegEx even to determine if well formed; and there's no way RegEx will evaluate it.
You need an expression parser.
There are many articles here on CodeProject on parsing.

ankurparikh 15-Apr-15 14:32pm

Hi Matt, looking to indicate if it is "well formed"

Sergey Alexandrovich Kryukov 15-Apr-15 14:00pm

This is not how RegEx works. You probably can get help if you specify exactly what you want to achieve.
—SA

ankurparikh 15-Apr-15 14:33pm

Hi Sergey, want to check / validate if condition within "if ( ) " are well formed.

Sergey Alexandrovich Kryukov 15-Apr-15 16:09pm

Regex will tell you that, throwing an exception is it is not well-formed. Please see my solution, it should work for you.
—SA

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OriginalGriff · Accepted Answer · 2015-04-15T08:04:00

Regular expressions are text matching tools: they do not evaluate strings , and they are very poor at syntactical analysis.

Basically, you can't do it with a regex - or if you can it'll be so silly that you can't maintain or probably even properly test it.

Instead, look at something like this: The expression evaluator revisited (Eval function in 100% managed .NET)[^] - which is designed to do that.

Sergey Alexandrovich Kryukov · Accepted Answer · 2015-04-15T08:02:00

Please see my comment to the question: this is not how Regular Expressions work.

Just one idea: you could use your language using Regex, Java or C#, whatever you are really using, to do the branching based on some condition. And then, you could have to different Regex objects, one for one branch, another for another. Isn't this simple? Could be more readable and maintainable, too. :-)

—SA

RegEx to validate conditions within if ()

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