Re: Usage of throw

From:

red floyd <no.spam@here.dude>

Newsgroups:

comp.lang.c++.moderated

Date:

Wed, 3 Oct 2007 16:37:31 CST

Message-ID:

<TjSMi.54848$Um6.10217@newssvr12.news.prodigy.net>

Olivier Delannoy wrote:

Hi all,
I am interesting in adding contextual information (such as file/line)
in debug mode and not in production mode. In order to do that I plan
on adding a macro of the form :

MY_THROW(exp) which is going to be translated into :
  - in release mode: throw (exp)
  - in debug mode: throw (exp).context(__FILE__, __LINE__)

In order to do that I need to make sure all my exception provide a
context method of the form :

class MyExp
{
...
public:
   MyExp& context(char* file, int line) { ... ; return *this;}
};

Now in a test program I do:

void f()
{
    MY_THROW(MyExp()); // In Debug mode: throw
(MyExp()).context(__FILE__, __LINE__);
}

int main()
{
try
{
     f();
}
catch(MyExp& e)
{
     // Do something with e
}
}

This program works nice but I don't feel confortable with this kind of
use of throw. Is it safe/portable accross compiler/ in respect of
standards to throw an exception as I do ?

Looks to be legal to me.

The one thing I'd do is have context take a const char* as the first
param instead of a char*.

Alternatively, have multiple constructors and instead of putting
MyExp() as the arg, try this:

class MyExp {
    public:
        MyExp() { /* ... */ }
        MyExp(const char *file, const char *line) { /* ... */ }
    // ...
};

#ifdef DEBUG
#define MY_THROW(type) throw(type(__FILE__,__LINE__))
#else
#define MY_THROW(type) throw(type())
#endif

int main()
{
   try {
     MY_THROW(MyExp);
   }
   catch (MyExp&)
   {
   ]
}

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