c++

Destructor

school

When and how to use destructor?

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~Mystring()
{
	cout << "invoking destructor, clearing up" << end;
	if(buffer != NULL)
		delete [] buffer;
}

Whenever an object is out of scope or is deleted via and then destroyed, system call the Destructor.

When using <char*> buffer area, you must control the memory allocation and release by yourself, I do not recommend it, instead of using < std::string >, which is class tool, they make the most of Constructor and Destructor.

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class Mystring //When you use <char*>, you can do like this which is similar to <std::String>
{
  private:
  	char* buffer;
  public:
  	Mystring(const char* inistString) //Constructor
    {
      if(initString != NULL)
      {
        buffer = new char(strlen(initString) + 1); //Allocating memory
        strcpy(buffer, initString);
      }
      else
        buffer = NULL;
    }
 	 ~Mystring() //Destructor will be invoked when object is over
		{
			cout << "invoking destructor, clearing up" << end;
			if(buffer != NULL)
					delete [] buffer;
		}
  
  int GetLength()
  {
    return strlen(buffer);
  }
  
  const char* GetString()
  {
    return buffer;
  }
};

int main()
{
  MyString sayHello("Hello from String class");
  cout << "String buffer in sayHello is "<< sayHello.GetLength();
  cout << " characters long"<< endl;
  
  cout << "buffer contains: "<< sayHello.GetString()<<endl;
}

In this program, you don’t need andin you main function, they are hidden in the String class.

  • Pay attention: Destructor couldn’t be overloaded. If you forget Destructor, compiler will create a dummy destructor and invoke it, but dummy destructor is NULL, which means it can’t release the memory allocated dynamically.
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