john sun wrote:[color=blue]
> Here is snippet code.
> class B contains class A and A1 as data member. when client code execute new
> B(), B construtor throw exception, ...
> C++ will call destrcutor of A and A1 seperately. This is very confusing.
> Since A1 and A are also on heap. How C++ track dow these member? Thanks!
>
> #include <stdio.h>
> #include <memory>
> using namespace std;
>
> class O
> {
> public:
> O(){};
> ~O(){};
> }
> ;
> class A1
> {
> O* o;
> public :
> A1()
> {
> o=new O();
> printf("in A1 ctor\n");
> }
> ~A1()
> {
> delete o;
> printf("in A1 dtor\n");
> };
> };
>
> class A
> {
> public :
> A(){printf("in A ctor\n");};
> ~A(){printf("in A dtor\n");};
> };
> class B
> {
>
> auto_ptr<A> a;
> A1 a1;
> public:
> B():a(new A)
> {
> throw 1;
> }
> ~B(){printf("in B dtor\n");}
> };
>
>
> int main(int argc, char* argv[])
> {
> try{
> B *b=new B();
> }
> catch(int)
> {
> printf("catch block\n");
> }
> return 0;
> }
>
>
> After running a1 and a destructor will be called. This confused me. Since b
> is created in heap, and a and a1 is also on heap, how come exception can
> call a1 and a's destructor.
> ...[/color]
For 'a1' it doesn't really matter whether it is "on heap" or on
something else. 'a1' is a member subobject of class 'B'. In other words,
'a' is not a standalone object, it is an integral part of 'B' object, it
is embedded in 'B' object. This immediately means that its destructor
will be called in this situation. Destructors for _all_ immediate
subobjects of class 'B' will be called if 'B::B()' throws an exception
the way it is thrown in your code.
This also applies to 'a', which is an 'auto_ptr' subobject of class 'B'.
'a's destructor ('auto_ptr::~auto_ptr') is called, which in turn
'delete's the 'A' object dynamically allocated in the constructor
initialization list.
--
Best regards,
Andrey Tarasevich
