Define a macro to be run at global scope without warnings

Question

The following code is OK, but I get a warning due to the extra ';' after INIT.

#define INIT \
    namespace Vars { \
      int a = 0; \
    }

INIT;

int main() { ... }

How can I fix this code, allowing the notation with the extra ';'?

Consider that INIT must be callable at global scope.

This looks like an XY problem. Why do you need to add a `;` there? Why do you need a macro in the first place? — Neil Kirk, Nov 01 '15 at 02:20
What compiler are you using? ideone c++14 did not complain for me. Although I am not sure of the warning level. http://ideone.com/4VzHaL — drescherjm, Nov 01 '15 at 02:23

Vittorio Romeo · Answer 1 · 2015-11-01T02:34:29.857

2

If you really want to force the semicolon, one possible workaround is defining an unused struct with a "unique" name, like this:

#define CAT_IMPL(m0, m1) m0##m1
#define CAT(m0, m1) CAT_IMPL(m0, m1)

#define INIT \
    namespace Vars { \
      \
    } \
    struct CAT(some_unique_name, __LINE__) \
    { } __attribute__((unused))

INIT;
INIT;

int main() { }

Coliru example here.

edited Nov 01 '15 at 02:34

answered Nov 01 '15 at 02:28

Vittorio Romeo

90,666
33
258
416

That's neat, but notice that it breaks compatibility with MSVC. – Christian Hackl Nov 01 '15 at 10:53
Thank you Vittorio, but I would say that instead of using that slightly cryptic code I prefer to get the warning. – Pietro Nov 02 '15 at 10:35
@Pietro: if you are satisfied, do you mind accepting this answer so that the question can be marked as "solved"? Thanks. Alternatively, you can post your own answer and accept it. – Vittorio Romeo Jan 07 '16 at 17:23

score 0 · Accepted Answer · answered Jan 08 '16 at 11:50

0

This solution seems to be reasonable:

#define INIT \
    namespace Vars { \
      int a = 0; \
    } int INIT_ = 0

INIT;

int main() { ... }

answered Jan 08 '16 at 11:50

Pietro

12,086
26
100
193

Define a macro to be run at global scope without warnings

2 Answers2