C++编写类String的构造函数、析构函数和赋值函数

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


class String
{
    public:
      String(const char *str = NULL); //普通构造函数 
      String(const String &other); //拷贝构造函数 
      ~String(); //析构函数
      String &operator =(const String &other); //赋值函数
    
    public:
      char *m_data; //用于保存字符串 



};



String::String(const char *str)
{
    if(str != NULL)
    {
        int len = strlen(str);
        m_data = new char[len+1];
        strcpy(m_data, str);
    }
    else 
    {
      m_data = new char[1]; //对空字符串自动申请存放结束标志'\0'的空
      *m_data = '\0';
    }
}



String::~String()
{
  delete [] m_data;
}



String::String(const String &other)
{
  int len = strlen(other.m_data);
  m_data = new char[len+1];
  strcpy(m_data, other.m_data);
}



String & String::operator=(const String &other)
{
  if(this == &other) //检查自赋值
  {
    return *this;
  }
  delete [] m_data; //释放原有的内存资源
  int len = strlen(other.m_data);
  m_data = new char[len+1];
  strcpy(m_data, other.m_data);
  return *this; //返回本对象的引用
}
int main()
{
  String str("hanyufeng");
  const String s1="liuyifei";
  const char s2[]="liushishi";
  printf("%s\n",str.m_data);
  printf("s1: %s\n",s1.m_data);
  String ss2(s2);
  printf("ss2: %s\n",ss2.m_data);
  String ss1(s1);
  printf("ss1: %s\n",ss1.m_data);
  return 0;
}