CODEWITHSUNDEEP
c++regexc++11
Aryan
Aryan

Reputation: 2745

regular expression in c++ 11

I wrote this line fore regex in c++ 11:

regex a("(\\w\\d)+(\\W)?(*)(\\W)?(\\w\\d)+");

I want to find phrase like A * B (A or B could be number) and space are optional

but at this line it throw an exemption! what wrong whit this line of code?

Upvotes: 0

Views: 211

Answers (2)

Jerry
Jerry

Reputation: 71598

Escape the asterisk (not sure if it should be escaped with a single or double backslashes, but correct me if I'm wrong!):

regex a("(\\w\\d)+(\\W)?(\\*)(\\W)?(\\w\\d)+");
                         ^^

The asterisk is a character in regex to indicate the occurrence of a character or group of characters 0 or more times.

Using (*) alone isn't valid, and causes the "exception" :)

Still though, to make it work, you need this regex:

regex a("(\\w)+(\\W)?(\\*)(\\W)?(\\w)+");

This should match your string A * B

\w (or \\w) in your case matches both numbers and alphabets, so don't worry about using \\d, because the way you wrote it, it will match one alphanumeric character (or underscore) accompanied with a digit.

Last, if you only want to match and not capture, this should still work:

regex a("\\w+\\W?\\*\\W?\\w+");

Addendum:

regex rx{ R"((\w)+\W?(\*)\W?(\w)+)" };
cout << regex_replace("A * B", rx, "($1$2$3)");

Upvotes: 6

Steve
Steve

Reputation: 7271

* is a reserved character in regex that will match a character 0 or many times. You need escape the * character using \\* to match the * symbol

E.g.

regex a("(\\w\\d)+(\\W)?(\\*)(\\W)?(\\w\\d)+");

Upvotes: 1

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