Question

I’m trying to match a C/C++ function definition using a fairly complex regular expression. I’ve found a case where it’s not working and I’m trying to understand why. Here is the input string which does not match:

   void Dump(const char * itemName, ofstream & os)

which clearly is a valid C++ method declaration. Here is the RE:

   ^[^=+-|#]*?([\w<>]+\s+(?!if|for|switch|while|catch|return)\w+)\s*\([^;=+-|]*$

This basically tries to distinguish between other C syntax which looks like a method declaration, i.e. which has words followed by paraentheses.

Using the very useful Python regular expression debugger (http://www.pythonregex.com/) I’ve narrowed it down to the trailing “$” – if I remove the trailing $ in the regular expression, it matches the method signature above; if I leave in the $, it doesn’t. There must be some idiosyncracy of Python RE’s that is eluding me here. Thanks.

Answer 1

The use of +-| in your character class [^;=+-|] is a range specification. This will result in the character class containing (actually excluding since you’re using ^) much more than you intend. To specify a literal - in a character class, mention it first like [^-;=+|].