#define statements within a namespace

Question

If I have a #define statement within a namespace as such:

namespace MyNamespace
{
  #define SOME_VALUE 0xDEADBABE
}

Am I correct in saying that the #define statement is not restricted to the namespace?

Is the following the "correct" thing to do?

namespace MyNamespace
{
  const unsigned int SOME_VALUE = 0xDEADBABE;
}

Answer 1

Correct,#define's aren't bound by namespaces. #define is a preprocessor directive - it results in manipulation of the source file prior to being compiled via the compiler. Namespaces are used during the compilation step and the compiler has no insight into the #define's.

You should try to avoid the preprocessor as much as possible. For constant values like this, prefer const over #define's.

Answer 2

I completely agree with the suggestions on the use of constants and the scope being unlimited for #defines.

However, if you do have to use preprocessor #define lines, please cover them up correctly for the expected scope,

namespace MyNamespace
{
  #define SOME_VALUE 0xDEADBABE
  // your code
  #undef SOME_VALUE
}

Why #defines?
I know one case where an embedded platform did not support constants in the code.
There was no way to initialize them...
It always helps to be more readable.

Answer 3

The preprocessor operates (conceptually at least, and often actually too) before namespaces and other language-level concepts "kick in" -- so yes, it's definitely much better to use language-level constructs such as const values wherever you can!