C++ 笔试题 string类

mystring.h

#pragma once
#include <iostream>

class MyString
{
public:
    MyString(const char *str=NULL);
    ~MyString();
    MyString(const MyString &other);
    MyString &operator=(const MyString &other);
private:
    char *m_str;
};

mystring.cpp

#include "mystring.h"

MyString::MyString(const char *str)
{
    if (str)
    {
        m_str = new char[strlen(str)+1];
        strcpy(m_str, str);
    }
    else
    {
        m_str = new char[1];
        *m_str = '\0';
    }
}

MyString::~MyString()
{
    if(m_str)
    {
        delete [] m_str;
        m_str = NULL;
    }
}

MyString::MyString(const MyString &other)
{
    if (m_str)
    {
        delete [] m_str;
        m_str = NULL;
    }
    m_str = new char[strlen(other.m_str)+1];
    strcpy(m_str, other.m_str);
}

MyString &MyString::operator=(const MyString &other)
{
    if(this != &other) //检查自赋值
    {
       if (m_str)
       {
           delete [] m_str;
           m_str = NULL;
       }
       m_str = new char[strlen(other.m_str)+1];
       strcpy(m_str, other.m_str);
    }
    return *this;
}