Developing environment: GNU GCC (g++) 4.1.2

While I'm trying to investigate how to increase 'code coverage - particularly function coverage' in unit testing, I've found that some of class dtor seems to be generated multiple times. Does some of you have any idea on why, please?

I tried and observed what I mentioned the above by using the following code.

In "test.h"

class BaseClass
{
public:
    ~BaseClass();
    void someMethod();
};

class DerivedClass : public BaseClass
{
public:
    virtual ~DerivedClass();
    virtual void someMethod();
};

In "test.cpp"

#include <iostream>
#include "test.h"

BaseClass::~BaseClass()
{
    std::cout << "BaseClass dtor invoked" << std::endl;
}

void BaseClass::someMethod()
{
    std::cout << "Base class method" << std::endl;
}

DerivedClass::~DerivedClass()
{
    std::cout << "DerivedClass dtor invoked" << std::endl;
}

void DerivedClass::someMethod()
{
    std::cout << "Derived class method" << std::endl;
}

int main()
{
    BaseClass* b_ptr = new BaseClass;
    b_ptr->someMethod();
    delete b_ptr;
}

When I built the above code (g++ test.cpp -o test) and then see what kind of symbols have been generated as follows,

nm --demangle test

I could see the following output.

==== following is partial output ====
08048816 T DerivedClass::someMethod()
08048922 T DerivedClass::~DerivedClass()
080489aa T DerivedClass::~DerivedClass()
08048a32 T DerivedClass::~DerivedClass()
08048842 T BaseClass::someMethod()
0804886e T BaseClass::~BaseClass()
080488f6 T BaseClass::~BaseClass()

My questions are as follows.

1) Why multiple dtors have been generated (BaseClass - 2, DerivedClass - 3)?

2) What are the difference among these dtors? How those multiple dtors will be selectively used?

I now have a feeling that in order to achieve 100% function coverage for C++ project, we would need to understand this so that I can invoke all those dtors in my unit tests.

I would greately appreciate if someone could give me the reply on the above.

First, the purposes of these functions are described in the Itanium C++ ABI; see definitions under "base object destructor", "complete object destructor", and "deleting destructor". The mapping to mangled names is given in 5.1.4.

Basically:

• D2 is the "base object destructor". It destroys the object itself, as well as data members and non-virtual base classes.
• D1 is the "complete object destructor". It additionally destroys virtual base classes.
• D0 is the "deleting object destructor". It does everything the complete object destructor does, plus it calls operator delete to actually free the memory.

If you have no virtual base classes, D2 and D1 are identical; GCC will, on sufficient optimization levels, actually alias the symbols to the same code for both.

I am currently trying to understand the new uniform initialization of C++0x. Unfortunately, I stumpled over using uniform initialization of references. Example:

int main() {
   int a;
   int &ref{a};
}

This example works fine:

% LANG=C g++ uniform_init_of_ref.cpp -std=c++0x -o uni -Wall -Wextra
uniform_init_of_ref.cpp: In function `int main()':
uniform_init_of_ref.cpp:3:10: warning: unused variable `ref' [-Wunused-variable]

(Update Comeau throws an error for that example, so maybe gcc shouldn't compile it as well)

Now, if I use a custom data type instead of an integer, it doesn't work anymore:

class Y
{};

int main()
{
    Y y;
    Y &ref{y};
}

% LANG=C g++ initialization.cpp -std=c++0x -o initialization -Wall -Wextra
initialization.cpp: In function `int main()':
initialization.cpp:9:13: error: invalid initialization of non-const reference of type `Y&' from an rvalue of type `<brace-enclosed initializer list>'
initialization.cpp:9:8: warning: unused variable `ref' [-Wunused-variable]

Unfortunately, I didn't find the relevant section in the standard draft. My guess is that I am misunderstanding the usage of uniform initialization, as Comeau complains with this message:

ComeauTest.c(9): error: reference variable "ref" requires an initializer
      Y &ref{y};

So, can someone of you point me in the right direction?

---

In case that you want to know why this question is relevant and why I don't just use Y &ref(y): I'd like to be able to use uniform initialization in the initialization list of a constructor:

class X { };

class Y {
    const X& x;

    public:
        Y (const X& xx):
            x{xx}
        {}
};

int main () {
    X x;
    Y y{x};
}

This fails with the same error message as above.

Note:

• I am using LANG=C to enable english error messages.
• gcc version: 4.6.1

According to N2672 the paragraph 8.5.4.4 should say:

Otherwise, if T is a reference type, an rvalue temporary of the type referenced by T is list-initialized, and the reference is bound to that temporary. [ Note: As usual, the binding will fail and the program is ill-formed if the reference type is an lvalue reference to a non-const type. ]

which (if I understand it correctly) means uniform initialization of references binds them to new anonymous instances, so it seems to me it's pretty useless. That still does not explain why one works and the other does not; they should behave the same (unless Y has some explicit constructors).