Special member functions

In the C++ programming language, special member functions 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).

• 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.

The compiler generated functions will be <code>public</code>, non-virtual and the copy constructor and assignment operators will receive <code>const&</code> parameters (and not be of the alternative legal forms).

Example

The following example depicts two classes: for which all special member functions are explicitly declared and for which none are declared.

Signatures

Here are the signatures of the special member functions:

C++03

In C++03 before the introduction of move semantics (in C++11) the special member functions were:

• Default constructor (if no other constructor is explicitly declared)
• Copy constructor
• Copy assignment operator
• Destructor

References