String类重写

#include <iostream>
#include<string.h>

using namespace std;
class String
{
    int length;
    int i;
private:
    char* m_data;//用于保护字符串  
public:
    String(const char *str=NULL)//普通构造函数
    {
        cout<<"调用了构造函数"<<endl;
        if(str==NULL)
        {
            length=0;
            m_data=new char(1);   //指针指向这段空间
            m_data[0]='\0';
        }
        else
            length=strlen(str);
            m_data=new char(length+1);
            strcpy(m_data, str); 
    }
    
    String(const String &other)//拷贝构造函数
    {
        cout<<"调用了拷贝函数"<<endl;

        if(m_data)
        {
            delete []m_data;
            int length=strlen(other.m_data);
            m_data=new char[length+1];
            strcpy(m_data, other.m_data);   
            }        
    }
    
    ~String(void)//析构函数
    {
        cout<<"调用了析构函数"<<endl;
        if (m_data) {
            delete []m_data;
        }
    }
    String &operator=(const String &other)//赋值函数
    {
        
        cout<<"调用了赋值函数"<<endl;
        if (this==&other)                  //检查自赋值
            return *this;
        
            delete []m_data;
            int length=strlen(other.m_data);
            m_data=new char[length+1];
            strcpy(m_data, other.m_data);
            return *this;    
    }

};


int main()
{
    String str("abc");
    String str1(str);
    str.operator=(str);
}