如何从使用花括号初始化的对象中捕获异常引发？

Question

I'm confronted to a problem. I have this :

int main()
{
    try
    {
        Class A obj;
    } 
    catch()
    {
     ...
    }
}

class B
{
    public:
        B(){throw an exception there from .cpp};
        ~B();
};

class A
{
    public:
        A();
        ~A();

     private:
        B objB{} // <=== Exception from there, how can I catch it ?
}

As you can see, I don't have any idea how can I get the exception when I initialize an object with curly braces from the header file.

Thank you :)

Answer 1

This live example demonstrates the technique of function-level try blocks.

A()
try {
   /* code */
} catch( exception e ) {
  throw e;
}

note, however, that you must throw an exception if the above construct catches something. It need not be the same exception. This is because the construction of A has failed (the exception has bypassed parts of the construction of A , and/or some subobject of A had its constructor terminated), and the only way to exit a constructor with a failed construction is via a throw .

Answer 2

I think this is not possible as such. Indeed, it is very similar to Avoid calling constructor of member variable and would leave the objB member of A not constructed. A solution is to split the constructor of B in two steps:

1. A default constructor that does nothing
2. A initialize method which trow the exception. You can pass the braces to that method.
3. B check that is is properly initialized before doing anything else.