破坏者不叫？

Question

由于某些原因，我试图跟踪该程序 流程结束，退出代码为4。 并结束而不打电话给破坏者？可能是什么原因？

#include <iostream>
using namespace std;

class A {
public:
    A() { cout << "A ctor" << endl; }
    A(const A& a) { cout << "A copy ctor" << endl; }
    virtual ~A() { cout << "A dtor" << endl; }
    virtual void foo() { cout << "A foo()" << endl; }
    virtual A& operator=(const A& rhs) { cout << "A op=" << endl; }
};

class B : public A {
public:
    B() { cout << "B ctor" << endl; }
    virtual ~B() { cout << "B dtor" << endl; }
    virtual void foo() { cout << "B foo()" << endl; }
protected:
    A mInstanceOfA; // don't forget about me!
};
A foo(A& input)
{
    input.foo();
    return input;
}
int main()
{
    B myB;

    B myOtherB;
    A myA;
    myOtherB = myB;
    myA = foo(myOtherB);
}

Answer 1

您的程序表现出未定义的行为，这是通过到达非void函数的闭合括号（此处为operator=）而没有遇到return语句。

Answer 2

对我来说（使用gcc 8.3.0）效果很好。但我收到警告：

test.cpp: In member function ‘virtual A& A::operator=(const A&)’:
test.cpp:10:63: warning: no return statement in function returning non-void [-Wreturn-type]
 virtual A& operator=(const A& rhs) { cout << "A op=" << endl; }

它会打印出来：

A ctor
A ctor
B ctor
A ctor
A ctor
B ctor
A ctor
A op=
A op=
B foo()
A copy ctor
A op=
A dtor
A dtor
B dtor
A dtor
A dtor
B dtor
A dtor
A dtor

也许您应该尝试解决警告。