笔试题string实现

笔试题string实现

#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include <string.h>
using namespace std;

class mystring{
public:
     mystring(const char *str = NULL);//构造函数
     mystring(const mystring &str);//拷贝构造函数
     ~mystring();//析构函数 
     mystring &operator=(const mystring &str);//运算符重载  
     int size() const;//字符串实际大小，不包含结束符
     const char *c_str() const;
     mystring operator+(const mystring &str) const;//重载+
      
private:
     char *data;
     int length;
};

mystring  mystring::operator+(const mystring &str) const {
    
    mystring newstr;
    newstr.length = length + str.size();
    newstr.data = new char[newstr.length + 1];
    strcpy(newstr.data, data);
    strcat(newstr.data, str.data);
    printf ("line:%d\n", __LINE__);
    cout << "this->data = " << newstr.data << endl;        
    return newstr;
}


mystring & mystring::operator = (const mystring &str) {
    if (this == &str)//检查自赋值
        return *this;
        
    if (data) 
        delete[] data;
    
    length = str.size();
    //length = strlen(str.data);
    data = new char[length + 1];
    strcpy(data, str.c_str());
    printf ("line:%d\n", __LINE__);
    cout << "this->data = " << this->data << endl;        
    
    return *this;
}

//通用构造函数
mystring::mystring(const char *str) {
    if (!str) {
        length = 0;
        data = new char[1];
        *data = '\0';
        
        printf ("line:%d\n", __LINE__);
    } else {
        length = strlen(str);
        data = new char[length + 1];
        strcpy(data, str);    
        
        printf ("line:%d\n", __LINE__);    
        cout << "this->data = " << this->data << endl;        
    }
}

//拷贝构造函数
mystring::mystring(const mystring &str) {
    length = str.size();
    data = new char[length + 1];
    strcpy(data, str.c_str());    
    printf ("line:%d\n", __LINE__);
    cout << "s3 = " << this->data << endl;
}

//析构函数
mystring::~mystring() {
    delete []data;
    length = 0;    
    printf ("line:%d\n", __LINE__);
}

//计算大小
int mystring::size() const {
    
    return length;
}

//将string转c_str()
const char *mystring::c_str() const {
    return data;
}

int main() {
    mystring s;
    printf ("line:%d\n", __LINE__);
    
    char a[] = "hello";
    char b[] = "world!";
    //通用构造函数
    mystring s1(a),s2(b);
    //拷贝构造函数
    mystring s3(s1);
    //+重载
    mystring s5 = s1 + s2;
    //赋值函数
    s1 = s2; 
    //拷贝构造函数
    mystring s4 = s1;
    
    
    
    return 0;
}