仿照string类，自己手动实现 My_string

代码如下

MyString.h

#ifndef MYSTRING_H
#define MYSTRING_H
#include <iostream>
#include <cstring>

using namespace std;

class My_string
{
private:
    char *ptr;         //指向字符数组的指针
    int size;           //字符串的最大容量
    int len;            //字符串当前容量


public:
    //无参构造
    My_string();

    //有参构造
    My_string(const char* src);
    My_string(int num, char value);
    //拷贝构造
    My_string(const My_string &other);
    //拷贝赋值
    My_string & operator= (const My_string &other);
    //析构函数
    ~My_string();
    //判空
    bool Isvoid();
    //显示
    void show();
    //尾插
    void push_back(char value);
    //尾删
    void pop_back();
    //at函数实现
    char &at(int index);
    //清空函数
    void clear();
    //返回C风格字符串
    char *data();
    //返回实际长度
    int get_length();
    //返回当前最大容量
    int get_size();


    //君子函数:二倍扩容
    bool Add();

};
#endif // MYSTRING_H

MyString.cpp

#include "MyString.h"

My_string::My_string():size(15)
{
    this->ptr = new char[size];
    this->ptr[0] = '\0';            //表示串为空串
    this->len = 0;
    cout<<"无参构造"<<endl;
}

//有参构造
My_string::My_string(const char* src):size(15) {
    this->ptr = new char[size];
    strcpy(ptr, src); // 复制字符串
    this->len = strlen(src);
    cout << "一个形参的有参构造" << endl;
}
My_string::My_string(int num, char value):size(15),len(num){
    if(num>15){
        cout<<"超出默认长度"<<endl;
        return;
    }
    this->ptr = new char[15];
    for(int i=0;i<num;i++){
        this->ptr[i] = value;
    }
    cout<<"部分形参的有参构造"<<endl;
}
//拷贝构造
My_string::My_string(const My_string &other):size(other.size),len(other.len){
    this->ptr = new char[size];
    strcpy(this->ptr, other.ptr); // 复制字符串
    cout<<"拷贝构造"<<endl;
}
//拷贝赋值
My_string& My_string::operator= (const My_string &other){
    if(this != &other){
        this->len =other.len;
        this->size = other.size;
        for(int i=0;i<other.len;i++){
            this->ptr[i] =other.ptr[i];
        }
    }
    cout<<"拷贝赋值"<<endl;
    return *this;
}
//析构函数
My_string::~My_string(){

    cout<<this->ptr<<"析构函数"<<endl;
    delete[] ptr;
}
//判空
bool My_string::Isvoid(){
    return this->len ==0 ? true:false;
}
//显示
void My_string::show(){
    for(int i=0;i<this->len;i++){
        cout<<*(this->ptr+i);
    }
    cout<<endl;
}
//尾插
void My_string::push_back(char value){
    if(this->len < this->size-1){
        *(this->ptr+len++) = value;
    }else if(this->Add()){
        *(this->ptr+len++) = value;
    }
}
//尾删
void My_string::pop_back(){
    this->len--;
}
//at函数实现
char& My_string::at(int index){
    if(index<=this->len-1){
        return this->ptr[index];
    }else {
        cout<<"下标越界"<<endl;
        exit(EXIT_SUCCESS);
    }
}
//清空函数
void My_string::clear(){
    free(this->ptr);
    this->ptr[0] = '\0';
    this->len = 0;
}
//返回C风格字符串
char* My_string::data(){
    return this->ptr;
}
//返回实际长度
int My_string::get_length(){
    return this->len;
}
//返回当前最大容量
int My_string::get_size(){
    return this->size;
}

bool My_string::Add(){
    if(this->len == this->size-1){
        char *p = new char[size*2];
        strcpy(p,this->ptr);
        free(this->ptr);
        this->ptr = p;
        return true;
    }else return false;
}

main.cpp

#include "MyString.h"

int main(){
    My_string s;
    cout<<"s：";
    s.show();
    My_string s1("hello");
    cout<<"s1：";
    s1.show();
    My_string s2(5,'A');
    cout<<"s2：";
    s2.show();

    My_string s3 = s2;
    cout<<"s3：";
    s3.show();
    s3 = s1;
    cout<<"s3：";
    s3.show();
    if(s3.Isvoid()){
        cout<<"s3空"<<endl;
    }else cout<<"s3非空"<<endl;
    cout<<"尾插：";
    s3.push_back('a');
    s3.show();
    cout<<"尾删：";
    s3.pop_back();
    s3.show();
    cout<<"查看下标4的值："<<s3.at(4)<<endl;
    cout<<"清空s3函数"<<endl;
    s3.clear();
    cout<<"s3：";
    s3.show();
    cout<<"s1的C风格字符串："<<s1.data()<<endl;
    cout<<"s1的实际长度："<<s1.get_length()<<endl;
    cout<<"s1当前最大容量："<<s1.get_size()<<endl;
//    cout<<"s3的二倍扩容"<<endl;
//    char c =' ';
//    while(c!='#'){
//        cin>>c;
//        s3.push_back(c);
//    }
    //s3.show();
}

运行结果

思维导图