Re: compilation error when Base Constructor calling pure virtual method
On Jul 6, 9:18 pm, liam_herron <liam_her...@hotmail.com> wrote:
Why does this compile when I define the body of the constructor in the
header versus
when I define the body of the constructor in the cpp file?
// Works
class A
{
public:
A() {f();}
virtual ~A() {}
virtual void f() = 0;
int a1_;
};
// Generates Linker Error
class A2
{
public:
A2();
virtual ~A2() {}
virtual void f() = 0;
int a2_;
};
Whether it generates error is compiler implementation dependent.
Logically it should always generate an error. The virtual table is
generated during construction and released during destruction.
The standard states that a virtual call to a pure virtual function in
the constructor or destructor is undefined.
class A { ?virtual void f()=0; };
class B : public A { ?void f(){...} };
The class 'A' constructor is called before the class 'B' constructor,
so the pointer to the pure virtual function defined in class 'B' is
not in the table yet. The call to the virtual functions is undefined,
because at that point anything can happen.
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