C# Parsing Strings that contain Double Quotes and Single Quotes using Regular Expression

Question

I'm parsing multiple double quoted literal text from a Visual Basic 6 Source file. Some lines may have comments at the end of each statement. Each comment is preceded by a single quote. In addition, the literal text may have single quotes which I need to retain. The line below is an example of a statement with a comment at the end.

Example Line: MsgBox "Must enter at least 2 'characters' before doing a Healthcare Data Dictionary Search.", vbInformation, "Search HDD" 'This is a "comment".

The following Regular Expression will return:

Must enter at least 2 'characters' before doing a Healthcare Data Dictionary Search.
Search HDD
comment

The following Regular Expression will capture/parse multiple double quoted string literals, however it does not ignore double quoted strings that come after a single quote (within a comment).

Regular Expression: "([^""]*)(?:\.[^""\\])*"
C#-Style: @"""([^""""]*)(?:\.[^""""\\])*"""

I would like to be able to strip off the comment however if I look for a single quote, that single quote could potentially be in the double quoted string I want to keep, thus stripping off half the double quoted string.

Please let me know if this is not clear and I'll try to clarify.

Any suggestions?

If you are doing this for an entire Source file, you are unlikely to find a regular expression that will work for all cases - you'd probably be better off writing a parser. It may (or may not) be slightly slower, but you're likely going to run it just a few times and speed won't matter that much. Regular Expressions only work well when you have predictable and consistent patterns. — Wonko the Sane
I am writing a parser. This is just one piece if it. I've been trying to narrow down the string using a non regex solution to the point where I can use the solution above. I haven't had much luck though. I was hoping I might find something here that would help me. — GhostHunterJim
To clarify, I'm looking for a regex to handle line by line, not the entire file. — GhostHunterJim
So the example line is one that you're trying to solve, correct? — tsacodes

tsacodes tsacodes · Accepted Answer · 2015-08-26T14:40:59

I saw that you tagged this with c#. Why not use c# and LINQ to your advantage! Would something like the below work for you?

   var text = "MsgBox \"Must enter at least 2 'characters' before doing a Healthcare Data Dictionary Search.\", vbInformation, \"Search HDD\" 'This is a \"comment\".";

   //Use LINQ to count singlequotes
   var singleQuoteOccurences = text.Count(sq => sq == '\'');

   //If you have an odd number, that means a comment is at the end
   //so just strip off everything after that last quote
   if(singleQuoteOccurences % 2 == 1)
        text = text.Substring(0, text.LastIndexOf('\''));

Yields:

MsgBox "Must enter at least 2 'characters' before doing a Healthcare Data Dictionary Search.", vbInformation, "Search HDD"

This is something that you could easily encapsulate into a "StringVBTrailingComment(string line)" or something like that.

C# Parsing Strings that contain Double Quotes and Single Quotes using Regular Expression

1 Answers