Why do C++ objects have a default destructor?

It’s wrong to say that a compiler-generated default constructor takes no action. It is equivalent to a user-defined constructor with an empty body and an empty initializer list, but that doesn’t mean it takes no action. Here is what it does:

  1. It calls the base class’es default constructor.
  2. It initializes the vtable pointer, if the class is polymorphic.
  3. It calls the default constructors of all members that have them. If there is a member with some constructors, but without a default one, then it’s a compile-time error.

And only if a class is not polymorphic, has no base class and has no members that require construction, then a compiler-generated default constructor does nothing. But even then a default constructor is sometimes necessary for the reasons explained in other answers.

The same goes for the destructor – it calls base class’es destructor and destructors of all members which have them, so it isn’t true in general case that a compiler-generated destructor does nothing.

But memory allocation really has nothing to do with this. The memory is allocated before the constructor is called, and it is freed only after the last destructor has finished.

Related Posts:

  1. no default constructor exists for class
  2. c++: No instance of overloaded function?
  3. In C++ can constructor and destructor be inline functions?
  4. When is it safe to call this-> in constructor and destructor
  5. What does the explicit keyword mean?
  6. Java default constructor
  7. Struct Constructor in C++?
  8. C++ struct constructor
  9. What does the explicit keyword mean?
  10. Inheriting constructors
  11. Inheriting constructors
  12. how to define -std=c++11 as default in g++
  13. Writing a LinkedList destructor?
  14. C++ error: no matching constructor for initialization of
  15. How do I call the class’s destructor?
  16. Destructor for a linked List
  17. Java class “cannot be resolved to a type”
  18. Getting error: ISO C++ forbids declaration of with no type
  19. QltAW.png
  20. Error: No instance of constructor matches the argument list
  21. expected constructor, destructor, or type conversion before ‘(’ token
  22. C++ template constructor
  23. Destructor for Binary Search Tree
  24. expected identifier before string constant
  25. Creating an instance of class
  26. C++ Cannot call constructor directly in small example
  27. What is the best way to give a C# auto-property an initial value?
  28. C++ Destructors with Vectors, Pointers,
  29. Here is some error with my .h file which show [Error] unterminated #ifndef when I include my class template in it
  30. How do I print out the contents of a vector?
  31. Iterate through a C++ Vector using a ‘for’ loop
  32. ‘was not declared in this scope’ error
  33. Simple dictionary in C++
  34. Good input validation loop using cin – C++
  35. Are the C++ & and * operators inverses in all contexts?
  36. C++ for each, pulling from vector elements
  37. How do I erase an element from std::vector<> by index?
  38. Why use ‘glad’ library for opengl initialization? [duplicate]
  39. What does `*&` in a function declaration mean?
  40. (->) arrow operator and (.) dot operator , class pointer
  41. How to reverse an std::string? [duplicate]
  42. What is the C version of RMI
  43. Difference between ‘strcpy’ and ‘strcpy_s’?
  44. What is uintptr_t data type
  45. const int = int const?
  46. Undefined reference to vtable
  47. What is the difference between a static and const variable?
  48. What is move semantics?
  49. Using “super” in C++
  50. unsigned int vs. size_t
  51. How do I clear a C++ array?
  52. error: expected primary-expression before ‘)’ token (C)
  53. What does -> mean in C++?
  54. Is std::stoi actually safe to use?
  55. Visual Studio 2015 doesn’t have cl.exe
  56. Right way to split an std::string into a vector
  57. How to resize array in C++?
  58. Is there a destructor for Java?
  59. C++: std does not have member “string”
  60. Fatal error: ‘stdafx.h’ file not found
  61. How do I add the MinGW bin directory to my system path?
  62. What’s the syntax for declaring an array of function pointers without using a separate typedef?
  63. C++ cannot open source file
  64. Error C1083: Cannot open include file: ‘stdafx.h’
  65. How do you handle a “cannot instantiate abstract class” error in C++?
  66. How to cast the size_t to double or int C++
  67. How to get Current Directory?
  68. “used without template parameters”
  69. Reading from .txt file into two dimensional array in c++
  70. C++ Error ‘nullptr was not declared in this scope’ in Eclipse IDE
  71. C++ Simple hangman game
  72. “The system cannot find the file specified” when running C++ program
  73. Remove First and Last Character C++
  74. C++ Convert string (or char*) to wstring (or wchar_t*)
  75. Why is inherited member not allowed?
  76. Error: macro names must be identifiers using #ifdef 0
  77. Error: free(): invalid next size (fast):
  78. Error: free(): invalid next size (fast):
  79. Fastest way to Convert String to Binary?
  80. Reading data from file into an array
  81. LINK : fatal error LNK1561: entry point must be defined ERROR IN VC++
  82. Java Copy Constructor ArrayLists
  83. Trying to use int in getline
  84. Stack around the variable ‘ ‘ was corrupted
  85. The difference between cin.ignore and cin.sync
  86. casting int to char using C++ style casting
  87. How to print (using cout) a number in binary form?
  88. What is the job of autogen.sh when building a c++ package on Linux
  89. Using G++ to compile multiple .cpp and .h files
  90. LPCSTR, LPCTSTR and LPTSTR
  91. How to do std::string indexof in C++ that returns index of matching string?
  92. Modulo operator with negative values [duplicate]
  93. Finding the type of an object in C++
  94. C++ Simple Dice roll – how to return multiple different random numbers [duplicate]
  95. How can I get a file’s size in C++?
  96. Why can’t I make a vector of references?
  97. Is there a way to simulate the C++ ‘friend’ concept in Java?
  98. What does “-Wall” in “g++ -Wall test.cpp -o test” do?
  99. What does ‘return *this’ mean in C++?
  100. C++ equivalent of StringBuffer/StringBuilder?

Leave a Comment