在面向对象编程中，哪些函数调用在编译时没有被解析? [英] Which function calls are not resolved at compile time in object oriented programming?

问题描述

哪些函数调用在编译时解析，哪些在运行时解析?我在某处读到并非所有函数调用都在编译时解析，我不知道是哪个.

Which function calls are resolved at compile time and which ones at runtime? I read somewhere that not all function calls are resolved at compile time i dont know which.

推荐答案

虚拟函数调用机制在运行时解决.因为，在 C++ 中，指向派生类的指针与指向其基类的指针是类型兼容的.因此，要调用虚函数，必须知道基类指针所指向的构造对象(或实际下层对象)的实际类型，这只能在运行时解析.

Virtual function calling mechanisms are resolved at run-time. Because, in C++, a pointer to a derived class is type-compatible with a pointer to its base class. So, to call the virtual function, the actual type of constructed object( or the actual under lying object ) to which base class pointer is pointing to must be known, which can only be resolved at runtime.

struct foo
{
     virtual void virtualMethod()
     {
          cout<< " \n virtualMethod of foo \n";
     }

     void normalMethod()
     {
          cout<< " \n normalMethod of foo \n";
     }
     virtual ~foo() {}
};

struct bar: public foo
{
     void virtualMethod()
     {
         cout<< " \n virtualMethod of bar \n";
     }
     void normalMethod()
     {
          cout<< " \n normalMethod of bar \n";
     }
     ~bar() {}
};

foo* obj = new bar ;
obj->virtualMethod() ;

现在，由于 virtualMethod() 需要调用哪个取决于运行时类型(或实际底层对象)obj 指向，因为 obj 可以指向由 new foo 或 new bar 构造的对象.在运行时，我们知道obj是由一个返回类型为bar*的对象构造的，如果存在，则调用派生类的相应虚函数.否则调用基类虚函数.

Now, since which virtualMethod() needs to be called depends on the run time type( or the actual under lying object ) obj is pointing to because obj can be pointed to an object constructed by either new foo or new bar. At run-time, we know that that obj is constructed from an objected whose type returned is bar*, corresponding virtual function of the derived class is called, if exists. Else base class virtual function is called.

obj->normalMethod();

这个方法可以在编译时自己解析，因为它是一个普通的成员函数.

This method can be resolved at compile time itself because it's a normal member function.

结果:ideOne 结果链接

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