[C++] Enum declaration inside a scope that is a parameter of a macro.

Question

Hi,

I am trying to create a macro that takes a scope as a parameter.
I know, it is probably not a good thing etc etc.
I was trying this and got the problem that preprocessor looks for commas and parentheses... the problem is with enum.

How would I declare a enum inside a scope that is a parameter of a macro?

when the compiler see the comma between enum itens, it takes it as a separator.

If you are curious to know why I entered into this, is because I need to register my namespaces and classes, for namespaces I need to know when they are closed, so I was thinking to create a macro that initially calls a static function that register the namespace, encapsulate its contents and finally call a static function that removes the namespace from the registry.
With a macro it would be easier for the coder to do this and make sure he doesn't forget to remove the namespace in the end of the bracket.

Thanks,
Joe

EDIT:

I want a macro that accepts a scope as parameters:

#define MYMACRO(unkownscope) unknownscope

class MYMACRO({
   // please, don't take this code seriously, it is just an example so you can understand my question
});

now, if I try:

#define MYMACRO(unkownscope) unknownscope

class MYMACRO({
  enum {
    anything = 1,
    everything = 2
  };
});

it won't compile because of the comma inside the enum, because the compiler thinks it is a separator of the macro. It doesn't happen with commas inside parentheses, example:

 int a(){
    int x = anyfunction(1, 2);
 }

would compile normally because the comma is inside a double parentheses.

Sorry for not being able to explain earlier... my english is not that good and the words just keep skipping me =[

Ty for the answers!
Joe

Answer 1

It sounds like you are pushing the preprocessor beyond where it's willing to go. While it's not as elegant, how about breaking your macro in two (one pre- and one post-) and rather then passing a "scope" as parameter, you surround your scope with you pre- and post- macros.

So, if your macro looks something like:

SOMACRO({ ... });

You would instead do something like:

PRESOMACRO();
{ ... };
POSTSOMACRO();

Answer 2

#define SCOPED_STUFF(pre,post) pre; STUFF; post;

#define STUFF enum {a,b,c}
SCOPED_STUFF(a,b)
#undef STUFF

#define STUFF enum {q,r}
SCOPED_STUFF(c,d)
#undef STUFF

Answer 3

You are attempting to replicate RAII with a macro.

#define SCOPE(ns) NamespaceRegistrar _ns_rar(ns);
struct NamespaceRegistrar {
    std::string _ns;
    NamespaceRegistrar(const std::string& ns) : _ns(ns) { AcquireResource(_ns); }
    ~NamespaceRegistrar() { ReleaseResource(_ns); }
};


{
     SCOPE("Foo")
     // stuff
}

I have no idea what you are talking about with regard to enums.

Answer 4

You already noticed what the problem is, an article on boostpro.com sums the problem up.
There are work-arounds, but i'd go for utilizing Boost.Preprocessor.

Without knowing exactly what you're trying to achieve syntactically, something like this might be what you are looking for (edited to PP_SEQ):

#define MAKE_ENUM(Name, Seq) enum Name { BOOST_PP_SEQ_ENUM(Seq) }
MAKE_ENUM(foo, (a)(b)(c));