在 C++ 中实现赋值运算符重载
本文将介绍几种如何在 C++ 中实现赋值运算符重载的方法。
使用复制赋值运算符在 C++ 中实现重载的赋值运算符
C++ 提供了重载运算符的功能，这是在特定类上调用内置运算符时调用自定义函数的一种常用方法。这些功能应有一个特殊的名称，以 operator 开头，后跟特定的操作符符号本身。例如，可以使用名为 operator= 的函数来实现自定义赋值运算符。赋值运算符通常应返回对其左侧操作数的引用。请注意，如果用户未明确定义副本赋值运算符，则编译器会自动生成一个。当该类不包含在堆内存上手动赋值的任何数据成员时，生成的版本将具有足够的功能。它甚至可以通过将每个元素赋值给相应的对象成员来处理数组成员。但是，在处理动态内存数据成员时，它有缺点，如下面的示例代码所示。
#include <iostream>
#include <string>
#include <utility>
#include <vector>
using std::cout; using std::endl;
using std::vector; using std::string;
class Person {
public:
Person() {
name = new string;
surname = new string;
};
Person(string n, string s) {
name = new string(std::move(n));
surname = new string(std::move(s));
}
Person(Person &p) {
name = new string(*p.name);
surname = new string(*p.surname);
}
~Person() {
delete name;
delete surname;
}
void renamePerson(const string &n, const string &s) {
name->assign(n);
surname->assign(s);
};
void printPerson() {
cout << *name << " " << *surname;
}
private:
string *name;
string *surname;
};
int main() {
Person P1("Buddy", "Rich");
Person P2 = P1;
P1.printPerson();
cout << endl;
P2.printPerson();
cout << endl;
P1.renamePerson("Jay", "Roach");
P1.printPerson();
cout << endl;
P2.printPerson();
cout << endl;
Person P3;
P3 = P1;
P1.printPerson();
cout << endl;
P3.printPerson();
cout << endl;
P1.renamePerson("Liam", "White");
P1.printPerson();
cout << endl;
P3.printPerson();
cout << endl;
exit(EXIT_SUCCESS);
}
输出：
Buddy Rich
Buddy Rich
Jay Roach
Buddy Rich
Jay Roach
Jay Roach
Liam White
Liam White
上面的代码仅明确定义了复制构造器，当将 P1 对象的内容赋值给 P3 对象时，会导致不正确的行为。请注意，第二次调用 P1.renamePerson 函数的第二次调用不应该修改 P3 对象的数据成员，但它修改了。解决方案是定义一个重载的赋值运算符，即复制赋值运算符。下一个代码片段实现了 Person 类的版本，该版本可以正确地复制赋值同一类的两个对象。但是请注意，复制赋值功能中的 if 语句可确保即使将对象赋值给自身，操作符也可以正常工作。
#include <iostream>
#include <string>
#include <utility>
#include <vector>
using std::cout; using std::endl;
using std::vector; using std::string;
class Person {
public:
Person() {
name = new string;
surname = new string;
};
Person(string n, string s) {
name = new string(std::move(n));
surname = new string(std::move(s));
}
Person(Person &p) {
name = new string(*p.name);
surname = new string(*p.surname);
}
~Person() {
delete name;
delete surname;
}
Person &operator=(const Person &p){
if(this != &p) {
*name = *(p.name);
*surname = *(p.surname);
}
return *this;
}
void renamePerson(const string &n, const string &s) {
name->assign(n);
surname->assign(s);
};
void printPerson() {
cout << *name << " " << *surname;
}
private:
string *name;
string *surname;
};
int main() {
Person P1("Buddy", "Rich");
Person P2 = P1;
P1.printPerson();
cout << endl;
P2.printPerson();
cout << endl;
P1.renamePerson("Jay", "Roach");
P1.printPerson();
cout << endl;
P2.printPerson();
cout << endl;
Person P3;
P3 = P1;
P1.printPerson();
cout << endl;
P3.printPerson();
cout << endl;
P1.renamePerson("Liam", "White");
P1.printPerson();
cout << endl;
P3.printPerson();
cout << endl;
exit(EXIT_SUCCESS);
}
输出：
Buddy Rich
Buddy Rich
Jay Roach
Buddy Rich
Jay Roach
Jay Roach
Liam White
Jay Roach
Founder of DelftStack.com. Jinku has worked in the robotics and automotive industries for over 8 years. He sharpened his coding skills when he needed to do the automatic testing, data collection from remote servers and report creation from the endurance test. He is from an electrical/electronics engineering background but has expanded his interest to embedded electronics, embedded programming and front-/back-end programming.
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