C++ - Inheritance type: public, protected, private

最新推荐文章于 2025-02-19 07:30:00 发布

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本文探讨了C++中不同继承类型（public、protected 和 private）如何影响基类成员的可见性和子类到基类的对象转换。通过具体示例说明了在不同继承方式下，编译器如何处理子类到基类的转换。

-- Members.

+------------+----------------+--------------+

| type | superclass + subclass |

+------------+----------------+--------------+

| public | public | public |

| public | protected | protected |

| public | private | N/A |

+-------------+---------------+---------------+

| protected | public | protected |

| protected | protected | protected |

| protected | private | N/A |

+-------------+---------------+---------------+

| private | public | private |

| private | protected | private |

| private | private | N/A |

+------------------------------+---------------+

-- Convert from sub-class to super-class

#include <cstdlib>
#include <stdio.h>
#include <iostream>

using namespace std;

class A {

public:

int i;
};

class B : protected A {   // public, protected, private
};

int main(int argc, char *argv[])
{

    B *b = new B();

    A * a = b;       // It will have a compiler error, it can be fixed by define class B is inherited from class A as public type.
    return 0;
}

The rule is: the conversion can work when there the super-class's public attribute can be accessed, i.e, when a->public_member(s) is readable; otherwise,

As for B, the super's member i is not accessable from out side since B is protected inherited from A, so if we can convert B to A, but the A's member i is defined as public, in other words, B's member i can be accessed through a pointer from class A; this is illegial with C++'s syntax.