Delete instance of class from DLL

Question

I am asking for help in implementing the proper freeing of memory in the dll library.

The structure of my project looks like this:

Library.dll:

• interface.h -> base class definition with pure virtual methods
• implementation.h -> derived class inheriting from public base
• implementation.cpp -> derived class methods definition

implementation.h contains also exported functions:

extern "C" __declspec(dllexport) Base* __stdcall Create()
{
    return new Derived;
}

extern "C" __declspec(dllexport) void __stdcall Delete(Base* B)
{
    delete B;
}

Apllication.exe code looks like this:

#include "interface.h"
#include "windows.h"
#include <iostream>
#include <memory>

typedef Base* (*CREATE_BASE)();
std::unique_ptr<Base> SmartPointer;

int main()
{
    // Load the DLL
    HINSTANCE dll_handle = ::LoadLibrary(TEXT("Library.dll"));
    if (!dll_handle) {
        std::cout << "Unable to load DLL!\n";
        return 1;
    }

    // Get the function from the DLL
    CREATE_BASE Fn = (CREATE_BASE)GetProcAddress(dll_handle, "Create");
    if (!Fn) {
        std::cout << "Unable to load Create from DLL!\n";
        ::FreeLibrary(dll_handle);
        return 1;
    }

// i have possibility to use only C++11 so creation of unique_ptr looks like this:
SmartPointer = std::unique_ptr<Base>(Fn());

// ... do something like SmartPointer->Action();
::FreeLibrary(dll_handle);
return 0;
}

The code above works and I can easily initialize the Base object and perform functions from the Derived class. Now i would like to use the exported "Delete" function as a custom pointer deleter now. So I prepared the definition of the type:

typedef void (*DELETE_BASE)(Base* B);

and I would like to use it more or less like this:

DELETE_BASE DeleteFn=(DELETE_BASE)GetProcAddress(dll_handle,"Delete");
SmartPointer = std::unique_ptr<Base>(Fn(),DeleteFn);

However, I get a compiler error that this unique_ptr definition is incorrect. How to fix this?

My current solution is based on:

• How to create a shared_ptr in dll and export it via a factory function?

Answer 1

The type of the deleter function must be specified since you want to override the default deleter (refer to std::unique_ptr<>).

Where you have used:

std::unique_ptr<Base>

you would instead want to use:

std::unique_ptr<Base, DELETE_BASE>