C++ 自定义string类重载相关运算符

叁歲伎倆 2022-05-31 22:54 188阅读 0赞

## c++提供的string类 ##

c++提供的string类可以做很多事情，它本质上是也是类，它的很多运算符都是通过重载进行实现的。

今天我们自己来简单来实现MyString类来模拟 string类能做得一些事情。重载+、\[\]、==、!=、<<、>> 几个运算符。

写法和[自定数组类型重载相关运算符][Link 1]差不多，多了一个+ 拼接运算符重载。

## 代码展示 ##

### MyString.h ###

#pragma once
    #ifndef __MY_STRING_H__
    #define __MY_STRING_H__
    #include <iostream>
    using namespace std;
    
    class MyString
    {
    public:
    	MyString();
    	MyString(int len);
    	MyString(const char* str);
    	//拷贝构造函数
    	MyString(const MyString &another);
    
    	friend ostream& operator<<(ostream &cout, MyString& myString);
    	friend istream& operator >> (istream &cin, MyString& myString);
    	MyString& operator=(const MyString& another);
    	char& operator[](int index);
    	bool operator==(MyString& another);
    	bool operator!=(MyString& another);
    	MyString operator+(const MyString& myString);
    	~MyString();
    
    private:
    	int length;//实际字符个数
    	char* str;
    };
    #endif // !__MY_STRING_H__

### MyString.cpp ###

#include "MyString.h"
    
    MyString::MyString()
    {
    	this->length = 0;
    	this->str = NULL;
    }
    
    MyString::MyString(int len)
    {
    	//cout << "构造函数 MyString::MyString(int len)...." << endl;
    	this->length = len;
    	this->str = new char[len];
    	//初始位空串
    	memset(this->str, 0, len);
    }
    MyString::MyString(const char* str)
    {
    	//cout << "构造函数 MyString::MyString(const char* str)...." << endl;
    	if (str == NULL)
    	{
    		this->length = 0;
    		this->str = new char[1];
    		strcpy(this->str, "");
    		return;
    	}
    	this->length = strlen(str);
    	this->str = new char[this->length + 1];
    	strcpy(this->str, str);
    
    }
    //初始化时调用
    MyString::MyString(const MyString & another)
    {
    	//cout << "拷贝构造函数 MyString::MyString(const MyString & another)...." << endl;
    	this->length = another.length;
    	this->str = new char[this->length+1];
    	strcpy(this->str, another.str);
    }
    
    MyString & MyString::operator=(const MyString & another)
    {
    	//cout << "赋值运算符 MyString & MyString::operator=(const MyString & another)...." << endl;
    	// 防止自身赋值
    	if (this == &another)
    	{
    		return *this;
    	}
    
    	// 如果自身原来有空间，先释放
    	if (this->str != NULL)
    	{
    		delete[] this->str;
    		this->str = NULL;
    		this->length = 0;
    	}
    
    	// 新开辟空间进行内容拷贝
    	this->length = another.length;
    	this->str = new char[this->length + 1];
    	strcpy(this->str, another.str);
    	return *this;
    }
    
    char& MyString::operator[](int index)
    {
    	return (this->str[index]);
    }
    
    bool MyString::operator==(MyString & another)
    {
    	if (this == &another)
    	{
    		return true;
    	}
    	if (this->length != another.length)
    	{
    		return false;
    	}
    	if (strcmp(this->str, another.str) != 0)
    	{
    		return false;
    	}
    	return true;
    }
    
    bool MyString::operator!=(MyString & another)
    {
    	return !(*this==another);
    }
    
    MyString MyString::operator+(const MyString& another)
    {
    	int len = this->length + another.length + 1;
    	MyString str1(len);
    	strcat(str1.str, this->str);
    	strcat(str1.str, another.str);
    	return str1;
    }
    
    MyString::~MyString()
    {
    	//cout << "~MyString()" << endl;
    	if (this->str != NULL)
    	{
    		delete[] this->str;
    		this->str = NULL;
    		this->length = 0;
    	}
    }
    
    ostream & operator<<(ostream & cout, MyString & myString)
    {
    	if(myString.str!=NULL)
    		cout << myString.str;
    	return cout;
    }
    
    istream & operator >> (istream & cin, MyString & myString)
    {
    	// 如果原来有字符串，将其清空
    	if (myString.str != NULL)
    	{
    		delete[] myString.str;
    		myString.str = NULL;
    		myString.length = 0;
    	}
    	//输入长度未知，用临时变量接收，然后进拷贝
    	char temp[1024] = { 0 };
    	cin >> temp;
    	int len = strlen(temp);
    	myString.length = len;
    	myString.str = new char[len + 1];
    	//注意：如果目标空间大于等于源字符串strcpy会复制到\0
    	strcpy(myString.str, temp);
    
    	return cin;
    }

### MyStringMain.cpp ###

#define _CRT_SECURE_NO_WARNINGS
    #include <cstdio>
    #include <iostream>
    #include "MyString.h"
    using namespace std;
    
    int main(int argc, char *argv[])
    {
    	MyString str1("hello");//构造函数
    	MyString str2("world");//构造函数
    	//cout << str1 << str2 << endl;
    	MyString str3 = str1;//调用拷贝构造函数
    	cout << str3 <<endl;
    	str3 = str2;// = 调用赋值运算符
    	cout << str3 << endl;
    	MyString str4 = str1 + str2;
    	cout << str4 << endl;
    	cout << "请重置str1和str2:";
    	cin >> str1 >> str2;
    	str4 = str1 + str2;
    	cout << str4 << endl;
    	MyString aa("aaa");
    	MyString bb("aaa");
    	cout <<"aa = " << aa<< ",bb = "<< 
    		bb <<",aa==bb:" << boolalpha << (aa == bb) <<endl;
    	return 0;
    }

## 运行结果 ##

![SouthEast][]

[Link 1]: http://blog.csdn.net/qq_29542611/article/details/79055917
[SouthEast]: /images/20220601/1ff59355cd8b4613aa6d518461672cc4.png