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Asked: 2026-05-22T22:42:34+00:00

EDIT: Apparently the question is not clearly formulated enough. The issue I am having

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EDIT: Apparently the question is not clearly formulated enough. The issue I am having is that when the destructor is defined in the header it gets added into multiple .obj files and the linker complains. The actual question is:

When I add the destructor to a CPP file in a DLL project and use the dll with dynamic loading and the interface header file, does the base destructor still get called to prevent leaking memory?

I am using MSVC 10.0 and have a DLL project that implements an interface. The interface is an abstract (pure virtual) base class. The idea is that the header is used with dynamic loading of the library. Therefore, I have used a pure virtual destructor to make sure the destructor in the base class gets called. Here is sample code to explain this:

//ISplitter.h
#pragma once

struct param {
    int something;
}

class ISplitter {
public:
    virtual ~ISplitter() = 0;
    virtual void useful() = 0;
}

ISplitter::~ISplitter() {
    /* Make sure base class destructor gets called */
}

And the main implementation header

//CSplitter.h
#pragma once
#include "CHelper.h"
#include "ISplitter.h"


class CSplitter : public ISplitter {
private:
    CHelper hlp;
public:
    ~CSplitter();
    void useful();
}

Some helper class

//CHelper.h
#pragma once
#include "ISplitter.h" // I need the struct

// Class definition should go here but is irrelevant

Now the problem is that the linker generates an error that tells me the destructor: ISplitter::~ISplitter(void) has been multiply declared and the system will not build.
Error:

CHelper.obj : error LNK2005: "public: virtual __cdecl ISplitter::~ISplitter(void)" (??1ISplitter@@UEAA@XZ) already defined in CSplitter.obj

What is the correct way to fix this? I have placed the destructor in ISplitter.cpp, but I am worried this may not work if I dynamically load the library and upcast the base class to ISplitter.

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1 Answer

  1. Editorial Team

    The problem is that the base class destructor always gets called- but in this case, you’ve made it pure virtual, so it doesn’t exist. The only reason to make a destructor pure virtual to is to enforce a class to be abstract when you have no other members. The destructor of a class needs to be defined in all cases.

    Edit: I mis-read your code. Just define the destructor virtually inline.

    virtual ~ISplitter() {}

    There’s no need for any pure virtual here, since you already have other pure virtual members.

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