move constructor

In some cases, object will be copied automatically:

class Mystring
{
  private:
  	char* buffer;
  public:
  	Mystring(const char* inistString) //Constructor
    {
      buffer = NULL;
      cout << "Default constructor: creating new MyString" << endl;
      if(initString != NULL)
      {
        buffer = new char(strlen(initString) + 1); //Allocating memory
        strcpy(buffer, initString);
        
        cout << "buffer points to: 0X"<<hex;
        cout << (unsigned int*)buffer <<endl;
      }
    }
  
  MyString(const MyString & copySource)//copy constructor
  {
    buffer = NULL;
    cout << "Copy constructor: copying from MyString" << endl;
    if(copySource.buffer != NULL)
    {
      //allocate own buffer
      buffer = new char [strlen(copySource.buffer) + 1];
      
      //deep copy from the source into local buffer
      strcpy(buffer, copySource.buffer);
     cout << "buffer points to: 0X" <<hex;
     cout << (unsigned int*)buffer << endl;
    }
  }
  
 	 ~Mystring() //Destructor
		{
			cout << "invoking destructor, clearing up" << end;
			if(buffer != NULL)
					delete [] buffer;
		}
  
  int GetLength()
  {
    return strlen(buffer);
  }
  
  const char* GetString()
  {
    return buffer;
  }
};

Mystring Copy(MyString & source) //func
{
  MyString copyForReturn(source.GetString());//create copy
  return copyForReturn;//reruen by value invokes copy constructor
}

int main()
{
  MyString sayHello("Hello World");
  MyString sayHelloAgain(Copy(sayHello));//invokes 2 times copy constructor
  
  return 0;
}

When instantiating ‘sayHelloAgain’, that will invoke func ‘Copy(sayHello)’, and the func return a MyString by Value, therefore invokes copy constructor twice. But, the value returned exist a short period, and not aviliable outside of the expression. So, it reduced performance.

That’s why here comes the Move constructor:

//move constructor syntax:
MyString(MyString && movesorce)
{
  if(movesource.buffer != NULL)
  {
    buffer = movesource.buffer; //take ownership
    movesorce.buffer = NULL; //set the move source to NULL
  }
}

This post will be update later.