C++: Pure Virtual Function Called

最近從水木C++版看到了這個問題，什麼情況下純虛函數會被調用？

這個連結解釋的比較清楚，http://www.artima.com/cppsource/pure_virtual.html

下面是一個demo，在基類構造函數中調用純虛函數，

>> cat pure1.C  
#include <iostream>
using namespace std;

class B {
public:
        B()
        {
                func();
        }
        void virtual func() = 0;
};

class D : public B {
public:
        void func() {
                cout << " I am in D " << endl;
        }
};

int main()
{
        D *pd = new D();
}
           

Solaris Sun CC,

>> CC pure1.C   
"pure1.C", line 8: Warning: Attempt to call a pure virtual function B::func() will always fail.
1 Warning(s) detected.

>> ./a.out
Pure virtual function called
Abort(coredump)
           

Linux g++

>> g++ pure1.C      
pure1.C: In constructor `B::B()':
pure1.C:8: error: abstract virtual `virtual void B::func()' called from constructor
           

在基類構造函數中間接調用純虛函數，

>> cat pure.C
#include <iostream>
using namespace std;

class B {
public:
        B()
        {
                fun();
        }
        void fun()
        {
                func();
        }
        void virtual func() = 0;
};

class D : public B {
public:
        void func() {
                cout << " I am in D " << endl;
        }
};

int main()
{
        D *pd = new D();
}
           

Linux g++,

>> g++ pure.C

>> ./a.out 
pure virtual method called
terminate called without an active exception
Abort(coredump)
           

Solaris Sun CC,

>> CC pure.C    

>> ./a.out
Pure virtual function called
Abort(coredump)