Using Const - Embarressed to Ask

Hi there,

Here's a noddy question. How do I use const to define constants instead of #define?

Everything I read tells me to use const instead of #define in C++, but I've yet to see an example. So...

How how do I declare a const int in a header file?

Can I declare (and define) a const inside a class header?

Cheers

I believe it's the same as a regular variable only you precede the whole statement with the const keyword.

e.g. const int pop = 213;

Can't do this? No?

Code:

---

class Test
{
public:
  const int A = 5;
};

---

RESULT:
[C++ Error] E2233 Cannot initialize a class member here

Try this instead:

Code:

---

class Test {
    pubilc:
        enum { A = 5 };
};

---

Const members (nonstatic) can ONLY be initialized in the initialization list

Code:

---

class Test
{
public:
Test();
private:
const int A;
};

Test::Test():
A(5)
{}

---

>Try this instead...

That's a nice idea. Thanks.

I've found I can do this in with BCB:

Code:

---

class Test {
    pubilc:
        static const int A = 5;
};

---

But it won't compile with VC6.

Is this a standards compliance issue?

Quote:

---

Originally posted by Davros
Can't do this? No?

Code:

---

class Test
{
public:
  const int A = 5;
};

---

RESULT:
[C++ Error] E2233 Cannot initialize a class member here

---

That won't work because when you just say
const int A
int class definition, that means you want A to be a const datamember of every instance of the class!

Instead, you have to make it a static const

Code:

---

class Test
{
public:
  static const int A = 5;
};

---

On a compliant compiler that should work, however, if you are using an old compiler (IE visual C++ 6.0) that will probably give you an error. So if your compiler is choking on that, you can use an enum instead

Code:

---

class Test
{
public:
  enum { A = 5 };
};

---

The only problem with that is it won't be of type int, but an unnamed integral enum type that can be implicitly converted to an int.

Edit: o man, late

Thanks.