Question

I have been running into strange linking behavior with g++, however, I’m just a student, and I was wondering if this was normal.

I am trying to link assembly code (machine: fedora 14 gnome 32bits x86 i686 intel i7) with c++ code and to have the assembly code call a method from a fonction instanciated in the c++ file. It seems that implementing a method in the class declaration will prevent it from being put in the linker table unless it’s used at least once in the original source.

class A
{
public:
    void showSUP() {
        cout<<"sup";
    }
};

After instanciating A, you will not be able to call _ZN1A7showSUPEv because it has not been put in the linking table:

call _ZN1A7showSUPEv

However, if you call A::showSUP() in the same .cpp as A was declared, then calling it from a seperate assembly file will work.

With (and instantiation of A)

class A
{
    void showSUP();
};

A::showSUP()
{
    cout<<"sup";
}

Calling _ZN1A7showSUPEv will work.

My question is, why doesn’t the first example work.

Thank you all in advance.

Answer 1

• For inlined functions the compiler
  will only output code where the function is used.
• Functions defined
  inside the class definition are
  inline (usually).
• The function isn’t
  used.
• Therefore: no function in the
  binary.