Quick and stupid question. How do I declare the size for an array if I'm not allowed to use global variables?
Suppose I have the file Album.h:
class Album {
private:
Song songs[MAX_SONGS];
//...
}
where do I put MAX_SONGS = 30?
const int MAX_SONGS = 30
is considered a variable right?
Please notice that the size should be known to the entire program.
class Album {
private:
static const int MAX_SONGS = 100;
Song songs[MAX_SONGS];
//...
};
Note that inline initialization of static const variables is only allowed for those whose type is integral. Also note that regardless of initialization, this is still just a declaration and not the definition. You won't generally need the definition, although there are certain cases when you would.
As for the visibility, you can provide a static getter function that would return MAX_SONGS.
public:
static int GetMaxSongs() { return MAX_SONGS; }
MAX_SONGS must be public, per OP's requirement.
std::array<Song, MAX_SONGS> songs; -- then you can use songs.size() for querying, at no cost.
const int MAX_SONGS = 30is considered a variable right?
Yes, MAX_SONGS is a variable, but it is a constant variable. It can't change.
It's not so much that global variables are inadvisable, it's that global mutable state is inadvisable, if it can be avoided. There is no mutable state here: MAX_SONGS cannot change.
MAX_SONGS is a constant expression. Consider an alternative extern const int MAX_SONGS; with an initializer in some other TU would not be a constant expression even if it is a constant variable.
MAX_SONGS is an object and because it has a name it is a variable. It is therefore a global variable and because it is const-qualified (and because, as Charles points out, it is initialized in its declaration) it is a constant. It is, in fact, a constant variable. @LuchianGrigore: The OP implied that he intended to declare MAX_SONGS either at namespace scope or as a static class member (otherwise, there's no way to consider it a global variable at all).You could also use the #define preprocessor comand.
in Album.h
#define MAX_SONGS 30
in Album.cpp
#include "Album.h"
class Album {
private:
Song songs[MAX_SONGS];
//...
}
To avoid static usage, use enum:
class Album {
private:
enum { MAX_SONGS = 30 };
Song songs[MAX_SONGS];
//...
}
const int MAX_SONGS = 30;is considered to be aconstant. You could also use a#define MAX_SONGS 30pre-processor directive.std::vector<Song>and you don't have to define a max size.