C++ 第四讲

参考string，实现mystring

#include <iostream>
#include <cstring>
using namespace std;

class myString
{
private:
    char *str; //记录c风格的字符串
    int size; //字符串实际长度

public:
    //无参构造
    myString():size(10) {
        cout << "无参构造 this = " << this <<endl;
        str = new char [size]; //申请空间
        strcpy(str, ""); //赋值为空串
    }
    //有参构造
    myString(const char *s){
        cout << "有参构造 this = " << this <<endl;
        size = strlen(s); //计算大小，不算\0
        str = new char [size+1]; //申请空间，含\0
        strcpy(str,s); //传进来的参数拷贝给str
    }
    //拷贝构造,初始化，参数：同类实例对象的引用，深
    myString(const myString & other){
        size = other.size;
        str= new char[other.size+1];
        strcpy(str,other.str);
        cout << "拷贝构造" << endl;
    }
    //析构函数
    ~myString() {
        delete str; //释放堆区空间
        cout << "析构函数 this = " << this<< endl;
    }
    //拷贝赋值函数，赋值，参数：同类实例对象，深拷贝，返回自身的引用,本质：赋值运算符
    myString &operator=(const myString &other){
        if(this != &other){
            this->str = new char[other.size +1] {*(other.str)};
            this->size = other.size;
            strcpy(str,other.str);
        }
        cout << "拷贝赋值函数" << endl;
        return *this;
    }

    //判空函数
    bool my_empty(const myString &other){
        return other.size;
    }
    //size函数
    size_t my_size(myString &other){
        return strlen(other.str);
    }
    //c_str函数
    char* my_str(myString &dest,const myString &src){
        dest.size = src.size;
        dest.str = strcpy(dest.str, src.str);
        return dest.str;
    }

    //at函数 char &at(int pos)
    char &at(int pos){
        return this->str[pos];
    }

    //加号运算符重载
    const myString operator+(const myString &sec)const{
        myString temp;
        temp.size = this->size+ sec.size;
        temp.str = strcat(this->str,sec.str);
        return temp.str;
    }

    //加等于运算符重载
    myString &operator+= (const myString &R){
//        char *temp = this->str;
//        delete []str;
//        this->size += sec.size;
//        this->str = new char[this->size + 1];
//        strcpy(this->str, temp);
//        temp[sizeof (temp) -1] = 'A';
//        strcat(this->str,sec.str);
//        return *this;

        int s_size = size + R.size;
        char *s_str = new char[s_size + 1];
        strcpy(s_str,str);
        strcat(s_str,R.str);

        delete[] str;
        str = s_str;
        size = s_size;
        return *this;
    }


    //关系运算符重载 （>）
    bool operator> (const myString &sec)const {
        return strcmp(this->str,sec.str);
    }

    //遍历
    void show(){
        cout << "str = " << str << " size = " << size << endl;
    }

};



int main()
{

    myString s1; //无参构造
    myString s2("hello world"); //有参构造
    myString s3(s2); //拷贝构造
    myString s4;
    s4 = s2; //加号
    myString s5("long time no see ");
    s5 += s2;   //加等
    cout << "s1 >>> ";
    s1.show();
    cout << "s2 >>> ";
    s2.show();
    cout << "s3 >>> ";
    s3.show();
    cout << "s4 >>> ";
    s4.show();
    cout << "s5 >>> ";
    s5.show();
    if(s2>s4){
        cout << "yes" << endl;
    }else {
        cout << "no" << endl;
    }

    return 0;
}