NULL指针能够访问类成员函数 [英] NULL pointer able to access class member function

问题描述

可能重复：

在NULL指针上访问类成员

一个非常愚蠢的问题，也可能是我的概念上的疑问。

A very silly question or may be my conceptual doubt.

    #include <iostream>

    using namespace std;

    class A
    {
            public:
            void print()
            {
                    cout<<"Printing\n";
            }
    };

    int main()
    {
            A * a = NULL;
            a->print();
            return 0;
    }

输出结果是：Printing

The output is: Printing

如何 a 指针（它为NULL）能够访问类A的成员函数。

How is a pointer(which is NULL) able to access member function of class A.

请解释...可能是它只是一个愚蠢的问题，但我有一个NULL指针不会访问类的成员函数。

Please explain... may be its just a silly question but I had the impression that a NULL pointer will not access the class's member function.

推荐答案

解释一个 NULL 指针，就像在代码中一样，是未定义的行为。这种 的可能性之一是它可能只是工作。

Dereferencing a NULL pointer, as you do in your code, is undefined behavior. One of the possibilities of such undefinedness is that it may just work. But it may crash the next time, or do something totally unexpected.

因为你没有使用隐式的这个您的成员函数 print 中的参数似乎像 NULL 指针不需要 dereferenced。

Since you are not using the implicit this argument in your member function print, seems like such NULL pointer never needs to actually be dereferenced.

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