RAII (Resource Acquisition Is Initialization) pattern limitations

[George2]

Hello everyone,


Through my testing and study of RAII (Resource Acquisition Is Initialization) pattern, I think it can solve resource release issue in the following two situations,

1. Local function object (on stack);
2. Object (either on heap or stack) pointer by auto_ptr;

But it has the limitation that the object pointed by a normal pointer and allocated on heap (using new or new[]) can not be automatically released, either the function returns normally or during exception stack unwinding. Is that correct?


thanks in advance,
George

[weaknessforcats]

But it has the limitation that the object pointed by a normal pointer and allocated on heap (using new or new[]) can not be automatically released,

I'm not sure what you mean here. All heap allocations are released as part of stack unwinding and that includes calling destrcutors on all array elements.

That said, heap allocations in the current stack frame are not released. You need to catch the exception inside the function doing the throw, delete the heap allocations made in that function and rethrow the exception.

Bear in mind that a pointer cannot be deleted unless you are deleting the final copy of it. If you don't know this, then you can't delete. Here you use a reference counted handle.

Beware of auto_ptr. Generally, it does not work as expcected. See Effective STL by Scott Meyers.

[George2]

Hi weaknessforcats,


Two more comments,

1.

[quote=weaknessforcats]I'm not sure what you mean here. All heap allocations are released as part of stack unwinding and that includes calling destrcutors on all array elements.[quote=weaknessforcats]

Suppose there is code like this,

void f()
{
    int* p = new int[10];
 
    // exception here
}
 

How will the memory allocated and pointed by p released automatically during stackl unwinding? We have to explicitly delete it in exception handler -- and RAII pattern does not use the explicit catch block at all. :-)

2.

Beware of auto_ptr. Generally, it does not work as expcected. See Effective STL by Scott Meyers.

Sorry that I do not have the book at hand. Could you show some major ideas and insights please?


regards,
George

[weaknessforcats]

No amount of comments by me is going to be satisfactory here. You need to read the statements made by other professionals. To develop in C++ you absolutely need textbook references.