在多重担任(multiple inheritance)中, 大概呈现多个基类担任自同一个基类, 即"菱形担任", 会导致最顶层的基类, 被复制多次;
可以回收虚担任(virtual inheritance)的方法, 使派生类(derived class)只保存最顶层基类的一个副本.
virtual, 即需要vptr(virtual table pointer), 即虚表指针, 特别占用4个字节;
代码如下:
/*
* test.cpp
*
* Created on: 2014.04.14
* Author: Spike
*/
/*eclipse cdt, gcc 4.8.1*/
#include <iostream>
#include <string>
using namespace std;
class File {private: int i[10];};
class InputFile : public File {};
class OutputFile : public File {};
class IOFile : public InputFile, public OutputFile {};
class vInputFile : virtual public File {};
class vOutputFile : virtual public File {};
class vIOFile : public vInputFile, public vOutputFile {};
int main () {
std::cout << "File = " << sizeof(File) << std::endl;
std::cout << "InputFile = " << sizeof(InputFile) << std::endl;
std::cout << "OutputFile = " << sizeof(OutputFile) << std::endl;
std::cout << "IOFile = " << sizeof(IOFile) << std::endl;
std::cout << "virtual InputFile = " << sizeof(vInputFile) << std::endl;
std::cout << "virtual OutputFile = " << sizeof(vOutputFile) << std::endl;
std::cout << "virtual IOFile = " << sizeof(vIOFile) << std::endl;
}
输出:
File = 40 InputFile = 40 OutputFile = 40 IOFile = 80 virtual InputFile = 44 virtual OutputFile = 44 virtual IOFile = 48
作者：csdn博客 Spike_King
