C++的拷贝函数和赋值函数既有联系又有区别，不细究的话很容易搞混，遂以小例示之如下，权作解惑之用
// test.cpp
#include <iostream>
#include <stdlib.h>
#include <algorithm>
using namespace std;
class Book
{
public:
Book(const char *name, const char*author, const double price): price(price) {
this->name = new char[strlen(name)+1];
this->author = new char[strlen(author)+1];
strcpy(this->name, name);
strcpy(this->author,author);
}
Book(const Book& book){
name = new char[strlen(book.name)+1];
author = new char[strlen(book.author)+1];
price = book.price;
strcpy(name, book.name);
strcpy(author, book.author);
}
Book& operator=(const Book& rhs) {
Book(rhs).swap(*this); // 先创建临时对象Book(rhs), 再调用下面的swap进行数据交换,
// 注意与*this交换数据的是临时对象, rhs并未修改，只是swap
// 结束后临时对象拥有了*this的数据， 而*this也拥有了由rhs
// 构造的临时对象的数据, 临时对象生命期结束时，*this的数据
// 会被销毁。
return *this;
}
~Book(){
delete[] name;
delete[] author;
}
private:
Book& swap(Book& rhs) {
double temp = rhs.price;
rhs.price = price;
price = temp;
std::swap(name, rhs.name); // std::swap()只是简单的交换指针的值
std::swap(author, rhs.author);
return *this;
}
public:
char* name;
char* author;
double price;
};
int main() {
Book a("The C++ standard library", "Nicolai M. Josuttis", 98);
Book b = a; // 对象b不存在， 拷贝构造函数在这里被调用
Book c("Emacs Lisp manual", "stallman", 0);
c = a; // c对象已经存在， 赋值函数(operator=)在这里被调用
cout << a.name << endl;
cout << a.author << endl;
cout << a.price << endl << endl;
cout << b.name << endl;
cout << b.author << endl;
cout << b.price << endl << endl;
cout << c.name << endl;
cout << c.author << endl;
cout << c.price << endl;
}
编译：
g++ -o test test.cpp
运行结果：
The C++ standard library
Nicolai M. Josuttis
98
The C++ standard library
Nicolai M. Josuttis
98
The C++ standard library
Nicolai M. Josuttis
98
