Can a class member function template be virtual?

Question

I have heard that C++ class member function templates can\'t be virtual. Is this true?

If they can be virtual, what is an example of a scenario in which one would

Answer 1

The following code can be compiled and runs properly, using MinGW G++ 3.4.5 on Window 7:

#include 
#include 

using namespace std;

template 
class A{
public:
    virtual void func1(const T& p)
    {
        cout<<"A:"<
class B
: public A
{
public:
    virtual void func1(const T& p)
    {
        cout<<"A<--B:"< a;
    B b;
    B c;

    A* p = &a;
    p->func1("A a");
    p = dynamic_cast*>(&c);
    p->func1("B c");
    B* q = &b;
    q->func1(3);
}

and the output is:

A:A a
A<--B:B c
A<--B:3

And later I added a new class X:

class X
{
public:
    template 
    virtual void func2(const T& p)
    {
        cout<<"C:"<

When I tried to use class X in main() like this:

X x;
x.func2("X x");

g++ report the following error:

vtempl.cpp:34: error: invalid use of `virtual' in template declaration of `virtu
al void X::func2(const T&)'

So it is obvious that:

• virtual member function can be used in a class template. It is easy for compiler to construct vtable
• It is impossible to define a class template member function as virtual, as you can see, it hard to determine function signature and allocate vtable entries.