Question

So I’m a beginner trying to get to grips with operator new. What’s wrong with my destructor?

class arr{
public:
    arr(){
        pool=::operator new(100*sizeof(double));
    }
    ~arr(){
        ::operator delete(pool);
    }
    void* pool;
};

int main()
{
    arr a;
    a.~arr(); //If I comment this out it's ok.

    void* pool2=::operator new(100*sizeof(double)); //Works
    ::operator delete(pool2); //Fine.

    system("pause");
    return 0;
}

Leaving a.~arr(); in gives me this error:

Debug assertion failed! File: dbgdel.cpp line: 52

Expression: _BLOCK_TYPE_IS_VALID(pHead->nBlockUse)

I can’t see why pool2 works fine but using the class gives me problems. Also the error only pops up after the system “pauses”, which is after a.~arr() is called???

Thanks!

Answer 1

Well, at a glance, you should not be explicitly calling the destructor. Instead use scoping to force a out of scope and call the destructor.

int main()
{
    {
        arr a;
    } //This calls destructor of a

    //Rest of code
}

Otherwise the destructor of a gets called twice: once when you call it and again when a goes out of scope.

EDIT:

Here ya go.

http://www.parashift.com/c++-faq-lite/dtors.html