Memory management of vector

Question

I have a C++ class with a private "pointer to vector" member pV, I assign a new vector to it in the constructor...

pV = new vector<FMCounter>(n, FMCounter(arg1))>;

However when I delete in the destructor of the class

delete pV;

I get a segfault and a message that I'm trying to free pv that wasn't allocated in the first place. I checked that pV->size() was 4K something, so I am sure it was allocated memory by new.

Try running your program under valgrind's memcheck - it will tell you where the memory was first freed or allocated when you do the second free. — Michael Ekstrand, Oct 02 '11 at 01:30
Why not just have the vector as a plain member? Otherwise see Christian's answer. — ergosys, Oct 02 '11 at 01:54

score 2 · Accepted Answer · edited May 23 '17 at 09:59

Pointer members with ownership semantics (allocating in constructor and deallocating in destructor) usually require to write a custom copy constructor and assignment operator (usually known as the Rule of Three), as the compiler generated ones will just copy the pointer member and not its underlying object. So if you at some point copy your containing object, you end up with two objects having the same pointer as member and the one destroyed secondly tries to delete an already deleted pointer.

At the simplest you should make sure your copy constructor does something like

TheClass::TheClass(const TheClass &rhs)
    : pV(new vector<FMCounter>(*rhs.pV))
{
}

and your assigment operator does something like

TheClass& TheClass::operator=(const TheClass &rhs)
{
    *pV = *rhs.pV
    return *this;
}

Memory management of vector

1 Answers1