C++（三十七） — 字符串的函数重载—案例

1、MyString.h 头文件

#pragma once

#include <iostream>
using namespace std;

class MyString
{
public:
    MyString();
    MyString(const char *p);
    MyString(const MyString& s);
    ~MyString();

public:
    MyString& operator=(const char* p);
    MyString& operator=(const MyString &s);
    char& operator[](int index);
    // 重载左移操作符、右移操作符，注意区别
    friend ostream& operator<<(ostream &out, MyString &s);
    friend istream& operator>>(istream &in, MyString &s);
    //重载双等号和不等号
    bool operator==(const char* p);
    bool operator!=(const char* p);
    bool operator==(const MyString& s );
    bool operator!=(const MyString& s);
    //重载大于和小于操作符
    int operator<(const char* p);
    int operator>(const char* p);
    int operator<(const MyString &s);
    int operator>(const MyString &s);
    
    // 把类的指针 单独使用,通过 s1.c_str() 来调用
    char *c_str()
    {
        return m_p;
    }

private:
    int m_len;
    char *m_p;
};

2、MyString.cpp 函数实现文件

#define  _CRT_SECURE_NO_WARNINGS
#include "MyString.h"


MyString::MyString()
{
    m_len = 0;
    m_p = new char[m_len + 1];
    strcpy(m_p, "");
}

MyString::MyString(const char *p)
{
    if (p == NULL)
    {
        m_len = 0;
        m_p = new char[m_len + 1];
        strcpy(m_p, "");
    }
    else
    {
        m_len = strlen(p);
        m_p = new char[m_len + 1];
        strcpy(m_p, p);
    }
}

//MyString s3 = s2;
MyString::MyString(const MyString& s)
{
    m_len = s.m_len;
    m_p = new char[m_len + 1];
    strcpy(m_p, s.m_p);
}

MyString::~MyString()
{
    if (m_p != NULL)
    {
        delete[]m_p;
        m_p = NULL;
        m_len = 0;
    }
}

MyString& MyString::operator=(const char* p)
{
    if (m_p != nullptr)//释放旧的内存
    {
        delete[] m_p;
        m_len = 0;
    }
    if (p == NULL) //根据p分配新的内存
    {
        m_len = 0;
        m_p = new char[m_len + 1];
        strcpy(m_p, "");
    }
    else
    {
        m_len = strlen(p);
        m_p = new char[m_len + 1];
        strcpy(m_p, p);
    }
    return *this;
}
MyString& MyString::operator=(const MyString &s)
{
    if (m_p != nullptr)//释放旧的内存
    {
        delete[] m_p;
        m_len = 0;
    }
    m_len = strlen(s.m_p);
    m_p = new char[s.m_len + 1];
    strcpy(m_p, s.m_p);
    return *this;
}

char& MyString::operator[](int index)
{
    return m_p[index];
}

ostream& operator<<(ostream &out, MyString &s)
{
    out << s.m_p;
    return out;
}
istream& operator>>(istream &in, MyString &s) {
    cin >> s.m_p;
    return in;
}

bool MyString::operator==(const char* p)
{
    if (p == nullptr)
    {
        if (m_len != 0)
        {
            return false;
        }
        else
            return true;
    }
    else
    {
        if (m_len == strlen(p))
        {
            return !strcmp(m_p, p);
        }
        else
            return false;
    }
}
bool MyString::operator!=(const char *p)
{
    return !(*this == p);
}

bool MyString::operator==(const MyString& s)
{
    if (m_len != s.m_len)
        return false;
    return strcmp(m_p,s.m_p);
}
bool MyString::operator!=(const MyString& s)
{
    return !(*this == s);
}
//if(s3<"bb"")
int MyString::operator<(const char* p){
    return strcmp(m_p, p);
}
int MyString::operator>(const char* p) {
    return strcmp(p, m_p);
}
int MyString::operator<(const MyString &s) {
    return strcmp(m_p, s.m_p);
}
int MyString::operator>(const MyString &s) {
    return strcmp(s.m_p, m_p);
}

3、test.cpp 测试文件

#include <iostream>
using namespace std;
#include "MyString.h"

//void main01()
//{
//    MyString s1;
//    MyString s2("s2");
//    MyString s2_2 = NULL;
//    MyString s3 = s2;
//
//    MyString s4 = "s4";
//    s4 = s2;
//    s4[1] = '9';
//    cout << s4[1] << endl;
//    cout << s4 << endl;//左移操作符的重载
//
//    system("pause");
//}
void main()
{
    MyString s1;
    MyString s2("s2");
    MyString s3 = NULL;
    cout << (s2 > "s") << endl;
    cin >> s2;
    cout << s2 << endl;
    system("pause");
}