How to write regex pattern to get a substring of a string in c# [closed]

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I need to extract a substring from a given string using regex.

I am parsing c# code, and I need to get the variable which is checked for null value.

Note: I save the c# code in a text file and read the lines as string value

My string could be in following format.

string code = "if (!(strOld_Value == "" && strNew_Value == "") || (strOld_Value == "" && strNew_Value.ToLower() != "") ";

From the above input string, I need to extarct the variable names, that are checked for null values. i.e) my desired output should be

strOld_Value == "" strNew_Value == "" strOld_Value == "" strNew_Value.ToLower() != ""

It is not necessary that my string will always in the same pattern, sometimes my string can be a simple one as follows,

string code = "if (Name == "")"

In the above case, my desired output is, Name == ""

Is it possible to write a generic regex pattern for this scenario? Thanks in Advance.

Sounds to me like you need to use/write a lexer/parser. Regex alone probably won't cut it here. — spender
– spender, Commented May 8, 2018 at 10:54
You can use Roslyn to get the AST of your code snippet and search for comparison operators: github.com/dotnet/roslyn/wiki/… — Good Night Nerd Pride
– Good Night Nerd Pride, Commented May 8, 2018 at 11:13

L. Guthardt · Accepted Answer · 2018-05-08 11:53:21Z

1

You can use the following regex pattern:

[_0-9a-zA-Z\s\.]+[()\s]*(==|!=)\s*\"[0-9a-zA-Z]*\"

edited May 8, 2018 at 11:53

L. Guthardt

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answered May 8, 2018 at 11:03

PftM

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2 Comments

FCin Over a year ago

It fails for e.g. if (var1 == "")

PftM Over a year ago

Include 0-9 in the variable name [_0-9a-zA-Z\s\.]+[()\s]*(==|!=)\s*\"[0-9a-zA-Z]*\"

VA systems engineer · Accepted Answer · 2018-05-08 11:24:18Z

1

As spender suggests, sounds like you need the ability to parse C# code and access the names of the variables identified by the parser

See S.O. How to programmatically parse and modify C# code

edited May 8, 2018 at 11:24

answered May 8, 2018 at 11:17

VA systems engineer

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Roman · Accepted Answer · 2018-05-08 11:32:49Z

1

You can try this regex:

(\w+(\.\w+[\)\(]*)*\s*(==|\!=)\s*\"\")

[\w]+ - matches any word character one or more times
(\.\w+[\)\(]*)* = (matches . and any word character after it, and there can be parentheses) zero or more times
\s* - optional space
(==|\!=) - == or !=
\s* - optional space
\"\" - matches empty value ("")

edited May 8, 2018 at 11:32

answered May 8, 2018 at 11:10

Roman

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