CODEWITHSUNDEEP
c++qtpimpl-idiom
kzsnyk
kzsnyk

Reputation: 2211

Pimpl and pointers in the implementation of the private class

I have the following Pimpl class where one of the member in the FooPrivate class is a pointer to a class A that should be dynamically allocated in Foo:init() and destroy in Foo:stop() or in the dtor of Foo. So far i have this :

foo.h :

#ifndef FOO_H
#define FOO_H

#include <QtGlobal>

class FooPrivate;

class Foo
{
public:
    Foo();
    void init(); // here we should dynamically instanciate an object of class A

    ~Foo();

private:
    Q_DISABLE_COPY(Foo)
    Q_DECLARE_PRIVATE(Foo)
    FooPrivate * const d_ptr;
};

#endif // FOO_H

foo.cpp :

#include "foo.h"
#include "foo_p.h"
#include "a.h"

Foo::Foo()
    : d_ptr(new FooPrivate)
{
    Q_D(Foo);

    d->a = nullptr; 
}

void Foo::init()
{
    Q_D(Foo);

    if (d->a) // init should happen only once
        return;

    // and d->a should be instanciated here
    d->a = new A;
}

void Foo::stop()
{
    Q_D(Foo);

    delete d->a;
    d->a = nullptr;
}

Foo::~Foo()
{
    Q_D(Foo);        

    delete d->a;
    delete d_ptr;
}

foo_p.h :

#ifndef FOOPRIVATE_H
#define FOOPRIVATE_H

class Foo;
class A;

struct FooPrivate
{
    FooPrivate() {}

    A *a;
};

#endif // FOOPRIVATE_H

My concern is about the ownership of A *a and where the allocation should take place in the code ? in Foo class or in FooPrivate ?

Is it more clean to create helper functions like FooPrivate::init() and FooPrivate::stop() that will be call from Foo:init() and Foo:stop(), and also delete A *a in the dtor of FooPrivate instead ?

Thank you.

Upvotes: 0

Views: 121

Answers (1)

Paul Evans
Paul Evans

Reputation: 27567

My concern is about the ownership of A *a

Then use a smart pointer, something like:

std::unique_ptr<A> a;

Upvotes: 1

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