[cfe-dev] C++ Language Support Library

[Howard Hinnant]

On Nov 10, 2008, at 12:55 PM, Sebastian Redl wrote:

> The most interesting part of the interoperability is exceptions. We  
> can claim to throw "GNUCC++\0" exceptions, and GCC code will be able  
> to catch them. But then we really have to match GCC exactly in all  
> relevant aspects (object layout, mostly).


I agree that this is a needed feature.

I have a <stdexcept> laying around that will do this.  It does not use  
std::string internally, so we are free to break abi with gcc's  
std::string (e.g. do a short string optimization).  However it does  
match the layout of gcc's exceptions which do use std::string  
internally.  It recreates a very limited ref-counted const  
std::string, layout compatible with gcc's std::string, non-templated  
(char-only), only has c_str() member (plus special members), not  
publicly exposed, 55 lines of code in all.  All each exception class  
exposes publicly is a void*.  E.g.:

class logic_error
     : public exception
{
private:
     void* __imp_;
public:
     explicit logic_error(const string&);
     explicit logic_error(const char*);

     logic_error(const logic_error&) throw();
     logic_error& operator=(const logic_error&) throw();

     virtual ~logic_error() throw();

     virtual const char* what() const throw();
};

Fortunately sizeof(gcc std::string) == sizeof(void*).

-Howard