C++ has several special member functions that are defined by the compiler even if not defined by the user. These special member functions are the default constructor, the copy constructor, the copy assignment operator, the move constructor, the move assignment operator, and the destructor. However, there are many rules for what is defined and in which circumstances. For instance, if no special member function is defined by the user then all of them are implicitly defined by the compiler. On the other hand, if a copy constructor or copy assignment operator is defined by the user, then the move constructor and move assignment operator are not defined by the compiler.
To make it easier to comprehend all the rules, the following table describes what is defined by the compiler based on what is defined by the user.
| Default constructor | Copy constructor | Copy operator= | Move constructor | Move operator= | Destructor | |
|---|---|---|---|---|---|---|
| Nothing | YES | YES | YES | YES | YES | YES |
| Any constructor | NO | YES | YES | YES | YES | YES |
| Default constructor | NO | YES | YES | YES | YES | YES |
| Copy constructor | NO | NO | YES | NO | NO | YES |
| Copy operator= | YES | YES | NO | NO | NO | YES |
| Move constructor | NO | DELETED | DELETED | NO | NO | YES |
| Move operator= | YES | DELETED | DELETED | NO | NO | YES |
| Destructor | YES | YES | YES | NO | NO | NO |
In the table above, on the horizontal, we have the special member functions that the compiler defines and on the vertical the functions the user may define. You should read the table as follows:
| YES | the special member function is defined by the compiler |
| NO | the special member function is not defined by the compiler |
| NO | the special member function is not defined by the compiler since it is defined by the user |
| YES | the special member function is defined by the compiler but this is deprecated and may be removed in the future |
| DELETED | the special member function is defined by the compiler as deleted |
Your table is incorrect, if the destructor is defined, the compiler does not generated move assignment. Generating copy construction/assignment in that case is also deprecated. https://i.stack.imgur.com/b2VBV.png.
There is a mistake in your table, if the destructor is defined by the user, then the move assignment operator is NOT defined by the compiler.
I think the table could therefore be simplified somewhat (less rows, less columns) by grouping together copy constructor and copy assignment operator and the one hand, and move constructor and move assignment operator on the other. It would be less scary.
Thanks for pointing to the error. I have fixed the table.
As a side note, the yellow YES means that the function is generated by the compiler but that is deprecated and may be removed in the future.
I dont see any colors. tries firefox chrome and ie.
Very hard to read this without the colors
Colors fixed!
Thank you! This is great. Just one correction – the [default constructor/default constructor] box should be gray