Question about static variables

[tpb]

When I said "if it was working properly" I didn't mean to suggest that it isn't proper for it to complain. Just that if what I was trying actually worked, it wouldn't have complained about the VLA (which I know is non-standard since I tell people that all the time).

Anyway, I obviously don't understand how extern and const work together. Perhaps they simply don't. So here'a s version of my original example that works.

// main.cpp
#include <iostream>
#include "settings.h"
#include "f.h"

int main() {
    std::cout << settings.a << '\n';
    f();
    std::cout << settings.a << '\n';

    int a[settings.c]{};
    for (int i = 0; i < settings.c; i++) std::cout << a[i] << ' ';
    std::cout << '\n';
}

// settings.h
#ifndef SETTINGS_H_
#define SETTINGS_H_

struct Settings {
    static int a;
    static int b;
    static const int c = 10;   // must be initialized here
};

extern Settings settings;

#endif


// settings.cpp
#include "settings.h"

int Settings::a = 1;
int Settings::b = 2;


// f.h
#ifndef F_H_
#define F_H_

void f();

#endif


// f.cpp
#include "settings.h"

void f() {
    settings.a = 42;
}

$ g++ -std=c++11 -Wall -Wextra -pedantic -c main.cpp
$ g++ -std=c++11 -Wall -Wextra -pedantic -c settings.cpp
$ g++ -std=c++11 -Wall -Wextra -pedantic -c f.cpp
$ g++ -std=c++11 -Wall -Wextra -pedantic main.o settings.o f.o
$ ./a.out
1
42
0 0 0 0 0 0 0 0 0 0 

[H00G0]

@tpb, & FurryGuy
Thanks a lot for taking the time to test and explain this out, this is very much appreciated!

So I guess I'd better either put my const in a structure or define them in the header file straight away.

It's nice to always keep learning bits here and there, Thanks guys <3!

[Peter87]

The size of stack-allocated arrays needs to be constexpr (i.e. a compile-time constant). const sometimes implies constexpr, but not always. If you have declared a variable as extern const, without defining it, the value is not known so it can't be constexpr.

[H00G0]

Thanks for the info Peter87, that makes sense