A private static data member in Cpp .. can only be initialized when it is defined, but invalid initialization in the class?

Question

Initialization in the header file causes the following error:

invalid in-class initialization of static data member of non-integral type 'bool [8]' 

if I try to initialize in .cpp, I get:

 'bool Ion::KeyboardInput::key [8]' is a static data member; it can only be initialized at its definition 

Here is the title:

 enum MYKEYS { KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT, KEY_W, KEY_S, KEY_A, KEY_D }; class KeyboardInput { public: KeyboardInput(); ~KeyboardInput(); static void getKeysDown(ALLEGRO_EVENT ev); static void getKeysUp(ALLEGRO_EVENT ev); static bool getKey(int keyChoice); private: static bool key[8] = {false, false, false, false, false, false, false, false}; }; 

Answer 1

The first error message tells you that initializing a static member variable in the header file is not correct. The second error message means that you tried to initialize the static member key in your constructor.

A static member variable of a class must be declared inside the class (without initialization) and then defined outside the class in the .cpp file (sort of like a global variable, except that the variable name has the class name included in it).

 bool KeyboardInput::key[8]; 

A variable definition may include an initializer. Since you initialized it for all false, the above definition in your .cpp file is sufficient.

A static member variable of a class is not too different from a global variable, except that it is limited to the class name and can only be protected for class members (with private ), immediate class subclasses (using protected ) or friends of the class.

Answer 2

You must declare the statics in the .h file and assign values ​​to it in the .cpp file. Something like that,

_header.h

 class KeyBoardInput{ public: KeyboardInput(); .... private: static bool key[8]; }; 

_header.cpp

 \#include<"_header.h"> bool KeyBoardInput::key[8] = {false, false, false, false, false, false, false, false}; 

Apart from the cpp file, you cannot initialize a static variable anywhere ... This does not apply to a specific object. Therefore, you must initialize outside the class (in the cpp file) so that all objects can share it.

Answer 3

Try the following:

 enum MYKEYS { KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT, KEY_W, KEY_S, KEY_A, KEY_D }; class KeyboardInput { public: KeyboardInput(); ~KeyboardInput(); static void getKeysDown(ALLEGRO_EVENT ev); static void getKeysUp(ALLEGRO_EVENT ev); static bool getKey(int keyChoice); private: static bool key[8]; }; bool KeyboardInput::key = {false, false, false, false, false, false, false, false}; 

The last line should really be placed in the .cpp file, since all the "code" should be in the cpp file.