C++ - 默认复制构造函数 执行 浅拷贝

默认复制构造函数 执行 浅拷贝

本文地址: http://blog.csdn.net/caroline_wendy/article/details/23941807

C++, 会默认生成一个复制构造函数, 当类中出现指针时, 复制会执行浅拷贝, 即只复制指针的地址, 不会复制数据;

所以在类中, 使用指针时, 需要注意; 如果想使用深拷贝, 可以添加复制构造函数.

以下代码, 如果不添加复制构造函数, 则会运行出错, 但可以通过编译, 

运行时, 因为删除(delete[])两次str所指的同一片地址空间, 所以程序无法执行.

代码:

/* * main.cpp * *  Created on: 2014.4.15 *      Author: Spike *//*vs2012*/#include <iostream>#include <cstring>#include <vector>#include <memory>using namespace std;class CDemo {public:CDemo() : str(NULL) {};~CDemo() {static int i=0;if (str) {std::cout << "&Demo" << i++ << " = " << (int*)this << ", str = " << (int*)str << std::endl;delete[] str;}}//复制构造函数CDemo(const CDemo& cd) {this->str = new char[strlen(cd.str) + 1];strcpy(this->str, cd.str);}char* str;};int main () {CDemo d1;d1.str = new char[32];strcpy(d1.str, "Caroline");std::vector<CDemo>* a1 = new std::vector<CDemo>();a1->push_back(d1); //执行复制构造函数std::cout << "d1.str = " << d1.str << std::endl;std::cout << "(*a1)[0].str  = " << (*a1)[0].str << std::endl;strcpy(d1.str, "Wendy");std::cout << "d1.str = " << d1.str << std::endl;std::cout << "(*a1)[0].str  = " << (*a1)[0].str << std::endl;delete a1;return 0;}

输出:

d1.str = Caroline(*a1)[0].str  = Carolined1.str = Wendy(*a1)[0].str  = Wendy&Demo0 = 0x312570, str = 0x312548&Demo1 = 0x22fec8, str = 0x312548