My_String类案例（构造、析构、重载'=' '[]' '<<' '==' '!=' '>' '<' '>>' 运算、操作符以及其他技巧）（重载完结）

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这是一个字符串类的小案例

头文件 MyString.h

#ifndef MYSTRING_H_INCLUDED#define MYSTRING_H_INCLUDED#include <iostream>using namespace std;//c中没有字符串 （字符串类  c风格的字符串）//空串class MyString{private:    int m_len;    char *m_p;    friend ostream& operator<<(ostream& out, const MyString &obj);    friend istream& operator>>(istream& in,  MyString &obj);public:    MyString();    MyString(const char *p);    MyString(const MyString &s);    ~MyString();    MyString& operator=(const MyString &obj);//用另一个的对象去等    MyString& operator=(const char *p);//用字符串去等    char operator[](int x);    bool operator==(const MyString &obj);    bool operator!=(const MyString &obj);    bool operator>(const MyString &obj);//与另一个对象去比较    bool operator>(const char *p);//与字符串去比较    bool operator<(const MyString &obj);//与另一个对象去比较    bool operator<(const char *p);//与字符串去比较public:    //技巧：怎么样把类的私有属性露出来    char* c_str()    {        return m_p;    }    //假设露出来的指针变成只读属性    const char* c_str2()    {        return m_p;    }    int length()    {        return m_len;    }};#endif // MYSTRING_H_INCLUDED

MyString.cpp

#include <string.h>#include "MyString.h"//无参构造函数//MyString s1;MyString::MyString(){    m_len = 0;    m_p = new char [m_len+1];    strcpy(m_p, "");}//有参构造函数//MyString s2("demo");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);    }}//拷贝构造函数//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);}//析构函数MyString::~MyString(){    if(m_p != NULL){        delete [] m_p;        m_p = NULL;        m_len = 0;    }}//重载 = 运算符//MyString s("fire");//t = s;//t = "cap";MyString& MyString::operator=(const MyString &obj){    if(m_p != NULL){//旧内存释放        delete [] m_p;        m_p = NULL;        m_len = 0;    }    m_len = obj.m_len;    m_p = new char[m_len+1];;    strcpy(m_p, obj.m_p);    return *this;}MyString& MyString::operator=(const char *p){    if(m_p != NULL){//旧内存释放        delete [] m_p;        m_p = NULL;        m_len = 0;    }    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);    }    return *this;}//重载 [] 运算符//cout << "t[1]: " <<t[1] << endl;char MyString::operator[](int x){    if(x < 0 || x >= m_len)        throw "询问越界";    else{        return m_p[x];    }}//重载 << 操作符// cout << s1 << s2 << s3 << t << endl;ostream& operator<<(ostream& out, const MyString &obj){    /*    for(int i = 0; i < obj.m_len; i++)        out << obj.m_p[i];    */    out << obj.m_p;    return out;}//重载 == 和 != 逻辑运算符bool MyString::operator==(const MyString &obj){    if(m_len != obj.m_len)        return false;    else{        for(int i = 0; i < m_len; i++)            if(m_p[i] != obj.m_p[i])                return false;    }    return true;}bool MyString::operator!=(const MyString &obj){    if((*this) == obj)        return false;    return true;}//重载 > < 运算符bool MyString::operator>(const MyString &obj){    for(int i = 0; i < m_len && i < obj.m_len; i++){        if(m_p[i] > obj.m_p[i])            return true;        if(m_p[i] > obj.m_p[i])            return false;    }    if(m_len > obj.m_len)        return true;    else        return false;}bool MyString::operator<(const MyString &obj){    if((*this) > obj || (*this) == obj)        return false;    return true;}bool MyString::operator>(const char *p){    int len = strlen(p);    for(int i = 0; i < m_len && i < len; i++){        if(m_p[i] > p[i])            return true;        if(m_p[i] > p[i])            return false;    }    if(m_len > len)        return true;    else        return false;}bool MyString::operator<(const char *p){    if((*this) > p || (*this) == p)        return false;    return true;}//重载 >> 操作符istream& operator>>(istream &in, MyString &obj){    if(obj.m_p != NULL){        delete [] obj.m_p;        obj.m_p = NULL;        obj.m_len = 0;    }    obj.m_p = new char[1000];    in >> obj.m_p;    obj.m_len = strlen(obj.m_p);    return in;}

main.cpp

#include <iostream>#include <string.h>#include "MyString.h"using namespace std;int main(){    //构造  and  析构    MyString s1;    MyString s2("demo");    MyString s3 = s2;    //重载 = 运算符    MyString t;    MyString s("fire");    t = s;    t = "cap";    //重载 [] 操作符    cout << "t[1]: " << t[1] << endl;    //重载左移操作符    cout << "s：" << s << "\ns1：" << s1 << "\ns2: " << s2 << "\nt: " << t << endl;    //重载 == 和 != 逻辑运算符    if(s1 == s2)    cout << "s1 " << "=="  << " s2" << endl;    else  cout << "s1 " << "!="  << " s2" << endl;    if(s1 != s2)    cout << "s1 " << "!="  << " s2" << endl;    else  cout << "s1 " << "=="  << " s2" << endl;    //重载 > 和 < 运算符    if(s1 > s2)     cout << "s1 > s2" << endl;    else{        if(s1 == s2)    cout << "s1 = s2" << endl;        else   cout << "s1 < s2" << endl;    }    //其他技巧    //假设我要实现： strcpy(s.m_p, "aaa111") 苦于指针是私有变量而无法实现    //技巧：怎么样把类的私有属性露出来    strcpy(s.c_str(), "f");//MFC    cout << "s：" << s << endl;    //重载 >> 操作符    //首先，我们要分配好内存（在构造函数中进行）    cout << "请用户输入 s ： ";    cin >> s;    cout << "s：" << s << endl;    return 0;}

下面是运行结果

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