Re: [Boost-users] [wave] preprocessing error

From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2007-06-22 13:51:27

Ovanes,

> thanks for the answer. I use VC Express 8.0 with boost 1.34, 
> wave comes from the release as well.
> May be the problem is on my side. My main looks like:
> 
> int main(int argc, char* argv[])
> {
> 	try
> 	{
> 		cmd_processor cmd(argc, argv);
> 		cmd.process();
> 	}

I'ld suggest to add a special catch for the Wave exceptions here:

      catch(boost::wave::cpp_exception const& e)
      {
          // ...
      }

This avoids to use dynamic_cast or other tricks.

> 	catch(std::exception const& e)
> 	{
> 		std::cerr << e.what() << nl << nl;
> 		return 2;
> 	}
> 	catch(...)
> 	{
> 		std::cerr << "Unknown exception occured..." << 
> std::endl;
> 		return 3;
> 	}
> 
>  	return 0;
> }
> 
> After the snippet specified I come into the case with 
> std::execption and e.what() returns boost::wave::preprocessor.
> 
> Debugging through what()... I came into the class 
> preprocess_exception and found additional methods, which give 
> me more info. Unfortunately, I rely on the standard 
> (std::exception) interface and don't like the idea of writing 
> hundres of 'if's or 'else if's or doing many 'dynamic_cast's 
> to distinguish exceptions. I believe that every exception 
> should give me enough description by calling the what 
> function. May be this is stupid... ;)

I hear your point! I tried to look around to get a feeling what other
libraries do and it seems the information returned by Wave's
exception::what() is not the best choice indeed (the standard is very vague
here: essentially it says 'what() should return a implementation defined
null terminated string'). What I'll do for the next verson of Wave (it's too
late for Boost V1.34.1) is to change the exception class to return a string
containing more complete descrption of the error (if you want to do
something on your local copy for now, just change the
preprocess_exception::what() function in cpp_exceptions.hpp to return
description()).

Regards Hartmut