昨天的一道面试题，分享下：
实现一个拷贝构造函数：
classFoo {
public:
Foo(A* a, B* b);
~Foo() {
delete a;
delete b;
}
// Implement copy constructor.
// Types A and B are Copy Constructible.
private:
A* a;
B* b;
};
答案：
Foo::Foo(const Foo& other)
{
this->a = new A(*other.a);
this->b = new B(*other.b);
}
备注：这道题主要考深度拷贝.
如果B会抛出异常，该如何处理？
答案：
Foo::Foo(const Foo& other)
{
this->a = new A(*other.a);
try{
this->b =new B(*other.b);
catch(…)
{
delete this->a;
this->a=nullptr;
}
}
如果不处理这个异常，会出现什么情况？如果是指针呢？
答案:内存泄露，如果是智能指针则不会出现内存泄露；
备注：这道题主要考如下知识点儿：
Objects Are Automatically Destroyed during StackUnwinding
When a block is exited during stack unwinding, the compilerguarantees that objects created in that block are properly destroyed.
If an exception occurs in a constructor, then the object underconstruction might be only partially constructed. Even if the object is onlypartially constructed, we are guaranteed that the constructed members will be properly destroyed.
由于智能指针有自己的析构函数，所以可以自动释放；但是使用new定义的指针就不行了，所以要内存泄露。