Catching exceptions from a constructor's initializer list

Question

Here's a curious one. I have a class A. It has an item of class B, which I want to initialize in the constructor of A using an initializer list, like so:

class A {
    public:
    A(const B& b): mB(b) { };

    private:
    B mB;
};

Is there a way to catch exceptions that might be thrown by mB's copy-constructor while still using the initializer list method? Or would I have to initialize mB within the constructor's braces in order to have a try/catch?

Answer 1

I don't see how you'd do that with initializer-list syntax, but I'm also a bit sceptical that you'll be able to do anything useful by catching the exception in your constructor. It depends on the design of the classes, obviously, but in what case are you going to fail to create "mB", and still have a useful "A" object?

You might as well let the exception percolate up, and handle it wherever the constructor for A is being called.

Answer 2

Have a read of http://weseetips.com/2008/06/04/how-to-catch-exceptions-from-constructor-initializer-list/

Edit: After more digging, these are called "Function try blocks".

I confess I didn't know this either until I went looking. You learn something every day! I don't know if this is an indictment of how little I get to use C++ these days, my lack of C++ knowledge, or the often Byzantine features that litter the language. Ah well - I still like it :)

To ensure people don't have to jump to another site, the syntax of a function try block for constructors turns out to be...

C::C()
try : init1(), ..., initn()
{
  // Constructor
}
catch(...)
{
  // Handle exception
}

Answer 3

It's not particularly pretty:

A::A(const B& b) try : mB(b) 
{ 
    // constructor stuff
}
catch (/* exception type */) 
{
    // handle the exception
}

Answer 4

It should be pointed out that this is NOT c++. This is part of mickysoft++.