C++ implements the String class instance code

C++ implements the String class instance code

This is a 10-point classic interview question, which can test whether students have a comprehensive grasp of C++ in a short time. The answer should include most of the knowledge of C++ class, ensuring that the String class can complete the functions of assignment, copy and variable definition.

#include<iostream> 
using namespace std; 
 
class String 
{ 
public: 
    String(const char *str=NULL); 
    String(const String &other); 
    ~String(void); 
    String &operator =(const String &other); 
private: 
    char *m_data; 
}; 
 
String::String(const char *str) 
{ 
  cout<<" The constructor is called "<<endl; 
  if(str==NULL)// Avoid wild Pointers, such as String b; If not, there would be wild  
         // Pointer to the  
  { 
    m_data=new char[1]; 
    *m_data=''/0''; 
  } 
  else 
  { 
   int length=strlen(str); 
   m_data=new char[length+1]; 
   strcpy(m_data,str); 
  } 
} 
String::~String(void) 
{ 
  delete m_data; 
  cout<<" The destructor is called "<<endl; 
} 
 
String::String(const String &other) 
{ 
 cout<<" The assignment constructor is called "<<endl; 
 int length=strlen(other.m_data); 
 m_data=new char[length+1]; 
 strcpy(m_data,other.m_data); 
} 
String &String::operator=(const String &other) 
{ 
   cout<<" The assignment function is called "<<endl; 
   if(this==&other)// If you copy yourself, you don't have to copy yourself  
         return *this; 
   delete m_data;// Deletes the pointer variable before it is pointed to in the assigned object 1 Two memory Spaces to avoid  
          // A memory leak  
   int length=strlen(other.m_data);// Calculate the length of the  
   m_data=new char[length+1];// To apply for space  
   strcpy(m_data,other.m_data);// copy  
   return *this; 
} 
void main() 
{ 
   String b;// Call constructor  
   String a("Hello");// Call constructor  
   String c("World");// Call constructor  
   String d=a;// Call the assignment constructor because it is in d Used during object creation a To initialize the  
   d=c;// Call the overloaded assignment function  
} 

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