default constructor

default constructor

Current Work:

1. Explicitly Defaulted and Deleted Functions in C++ 11

What is a Defaulted Function? Explicitly defaulted function declaration is a new form of function declaration that is introduced into the C++11 standard which allows you to append the ‘=default;’ specifier to the end of a function declaration to declare that function as an explicitly defaulted function. This makes the compiler generate the default implementations for explicitly defaulted functions, which are more efficient than manually programmed function implementations..

It is very important to note that A deleted function is implicitly inline. A deleted definition of a function must be the first declaration of the function. In other words, the following way is the correct way of declaring a function as deleted:

Top rule

2. The rule of three/five/zero

Rule of three If a class requires a user-defined destructor, a user-defined copy constructor, or a user-defined copy assignment operator, it almost certainly requires all three.

Because C++ copies and copy-assigns objects of user-defined types in various situations (passing/returning by value, manipulating a container, etc), these special member functions will be called, if accessible, and if they are not user-defined, they are implicitly-defined by the compiler.

The implicitly-defined special member functions are typically incorrect if the class manages a resource whose handle is an object of non-class type (raw pointer, POSIX file descriptor, etc), whose destructor does nothing and copy constructor/assignment operator performs a "shallow copy" (copy the value of the handle, without duplicating the underlying resource)..

Default Constructor

3. Default constructors

A default constructor is a constructor which can be called with no arguments (either defined with an empty parameter list, or with default arguments provided for every parameter). A type with a public default constructor is DefaultConstructible...

4. Constructors and member initializer lists

Constructor is a special non-static member function of a class that is used to initialize objects of its class type.

In the definition of a constructor of a class, member initializer list specifies the initializers for direct and virtual bases and non-static data members. (Not to be confused with std::initializer_list.)

A constructor must not be a coroutine. (since C++20) .

The body of a function definition of any constructor, before the opening brace of the compound statement, may include the member initializer list, whose syntax is the colon character :, followed by the comma-separated list of one or more member-initializers, each of which has the following syntax:

5. Special member functions

Special member functions[1] in C++ are functions which the compiler will automatically generate if they are used, but not declared explicitly by the programmer. The automatically generated special member functions are:

• Default constructor if no other constructor is explicitly declared.
• Copy constructor if no move constructor and move assignment operator are explicitly declared. If a destructor is declared generation of a copy constructor is deprecated (C++11, proposal N3242[2]).
• Move constructor if no copy constructor, copy assignment operator, move assignment operator and destructor are explicitly declared.
• Copy assignment operator if no move constructor and move assignment operator are explicitly declared. If a destructor is declared, generation of a copy assignment operator is deprecated.
• Move assignment operator if no copy constructor, copy assignment operator, move constructor and destructor are explicitly declared.
• Destructor
In these cases the compiler generated versions of these functions perform a memberwise operation. For example, the compiler generated destructor will destroy each sub-object (base class or member) of the object.
6. Special member function

The special member functions are class (or struct) member functions that, in certain cases, the compiler automatically generates for you. These functions are

1. the default constructor,
2. the destructor,
3. the copy constructor
4. and copy assignment operator,
5. and the move constructor
6. and move assignment operator.
If your class does not define one or more of the special member functions, then the compiler may implicitly declare and define the functions that are used. The compiler-generated implementations are called the default special member functions. The compiler does not generate functions if they are not needed.

You can explicitly declare a default special member function by using the = default keyword. This causes the compiler to define the function only if needed, in the same way as if the function was not declared at all.

In some cases, the compiler may generate deleted special member functions, which are not defined and therefore not callable. This can happen in cases where a call to a particular special member function on a class doesn't make sense, given other properties of the class. To explicitly prevent automatic generation of a special member function, you can declare it as deleted by using the = delete keyword...

7. C++ Special Member Function Guidelines

my Note:it has some good examples. The C++ special member functions are:

1. default constructor
2. copy constructor
3. move constructor
4. destructor
5. copy assignment
6. move assignment
8. Tutorial: When to Write Which Special Member

When explaining someone the rules behind the special member functions and when you need to write which one, there is this diagram that is always brought up. I don’t think the diagram is particularly useful for that, however.

It covers way more combinations than actually make sense. So let’s talk about what you actually need to know about the special member functions and when you should write which combination...

Good Standard

9. High Integrity C++ Coding Standard

12. Special Member Functions.

10. 11. Member Access Control

11. Member Access Control.

11. Special Member Functions

Virtual and Protected Destructors #

12. Non-static member functions

A non-static member function is a function that is declared in a member specification of a class without a static or friend specifier. (see static member functions and friend declaration for the effect of those keywords)

13. Tip of the Week #131: Special Member Functions and `= default`

Since the beginning of time, C++ has supported compiler-declared versions of some so-called special member functions: the default constructor, destructor, copy constructor and copy assignment operators. C++11 added move construction and move assignment to the list, and added syntax (=default and =delete) to give control over when those defaults are declared and defined..

14. Getting C++ Special Members Right

Things we need to get out of the way first.

15. Andrzej's C++ blog:: special memeber functions

Update. I no longer consider the advice given in this post a good one. I left it for reference, but I encourage you to also read this post.

You have probably already heard about the Rule of Zero formulated by R. Martinho Fernandes:

Classes that have custom destructors, copy/move constructors or copy/move assignment operators should deal exclusively with ownership. Other classes should not have custom destructors, copy/move constructors or copy/move assignment operators..
16. Declaring the move constructor

Update. I have updated the post a bit, as it misled a number of people to think that you need to define the move constructor in a cpp file. This is not so. I have now also highlighted another important feature of my solution: statically checked noexcept specification..

17. what are the necessary for special member funtions that should be declared?

This is a paragraph.

18. Rule-of-Three becomes Rule-of-Five with C++11?

This is a paragrapSo, after watching this wonderful lecture on rvalue references, I thought that every class would benefit of such a "move constructor", template MyClass(T&& other) edit and of course a "move assignment operator", template MyClass& operator=(T&& other) as Philipp points out in his answer, if it has dynamically allocated members, or generally stores pointers. Just like you should have a copy-ctor, assignment operator and destructor if the points mentioned before apply. Thoughts?.

19. C9 Lectures: Stephan T. Lavavej - Standard Template Library (STL), 1 of n

Welcome to another installment of C9 Lectures. In the following series, learn all about STL from the great Stephan T. Lavavej, Microsoft's keeper of the STL cloth (this means he manages the partnership with the owners of STL and Microsoft, including, of course, bug fixes and enhancements to the STL that ships as part of Visual C++).

In this first part, Stephan introduces STL and then demonstrates many of its core features (iterators, algorithms, and data structures). As is Stephan's nature, he elaborates on technical details in very substantive way. The Standard Template Library, or STL, is a C++ library of container classes, algorithms, and iterators. STL provides many fundamental algorithms and data structures. The STL is a general purpose library: its components are heavily parameterized such that almost every component in the STL is a template...