I cannot get one simple class to work

Hi!

I'm learning C++ programming. I got a problem with simple class.

Here is the code:

Code:

---

#include <iostream>
using namespace std;


class Menu
{
  int NUMMENUS = 0;
  char* labels [NUMMENUS];
  bool selected[NUMMENUS];

  public:
  void Setnum (int i) {
      NUMMENUS = i;
  };

  int Getnum()
  {
      return NUMMENUS;
  };
};

int main(void)
{
  Menu menu;

  menu.Setnum(8);

  cout<<"Number on: "<<menu.Getnum()<<"\n";
  return 0;
}

---

And here is the error:

Code:

---

leho@leho-laptop:~/Dokumendid/OpenGL/Menüü$ g++ teine.cpp -o teine
teine.cpp:8:18: error: invalid use of non-static data member ‘Menu::NUMMENUS’
    char* labels [NUMMENUS];
                  ^~~~~~~~
teine.cpp:7:17: note: declared here
  int NUMMENUS = 0;
                ^
teine.cpp:9:18: error: invalid use of non-static data member ‘Menu::NUMMENUS’
    bool selected[NUMMENUS];
                  ^~~~~~~~
teine.cpp:7:17: note: declared here
  int NUMMENUS = 0;
                ^

---

Where is the error?

Leho

> char* labels [NUMMENUS];
> bool selected[NUMMENUS];
Array sizes are compile time constants in C++.
You're trying to make it variable.

Perhaps you should be looking at say std::vector, which is something you can resize.

> int NUMMENUS = 0;

You can't initialise variables like that inside a class. Only const static qualified variables can.

Quote:

---

Originally Posted by Zeus_

> int NUMMENUS = 0;

You can't initialise variables like that inside a class. Only const static qualified variables can.

---

You can do that: it sets the default member initialiser, although the initialisation itself is only done when the constructor is invoked, i.e., when the initialiser list would be run.

Then my GCC is outdated because I sure do get an error if I try to write code like that.

For older versions of GCC, you might have to explicitly compile as C++11 with -std=c++11

Well, at least I think this is a C++11 feature; if it was introduced in C++14 then you might be stuck, and likewise if your version of GCC does not support C++11 (but if so, you should upgrade as that version of GCC is arguably obsolete).

To expand on Laserlight's point, one of the primary reasons to use GCC is that it is often first to implement current/new C++ features, so keeping one's GCC toolset current is usually quite important, though sometimes the most recent versions may be more difficult to install on some platforms. These days, on Windows with Visual Studio, Clang is much easier to use than GCC, while on Linux it is often easier to keep GCC current than it is for Clang.