[boost] BOOST_PP_EXPR_IF Behavior

From: John Eddy (johneddy_at_[hidden])
Date: 2005-02-02 15:34:45

I am not terribly familiar with the rules of the preprocessor.  Is it 
the case that the expression of the BOOST_PP_EXPR_IF macro is expanded 
regardless of the resulting value of the condition?

The reason I ask is because the following code produces a warning with 
VC7 .NET 2003.

#define 
MY_MACRO(array)                                                     \
    
BOOST_PP_EXPR_IF(                                                       \
        
BOOST_PP_ARRAY_SIZE(array),                                         \
        
BOOST_PP_TUPLE_TO_SEQ(                                              \
            
BOOST_PP_ARRAY_SIZE(array),                                     \
            
BOOST_PP_ARRAY_DATA(array)                                      \
        
)                                                                   \
    )

MY_MACRO((0, ()));

The warning is:

C4003: not enough actual parameters for macro 'BOOST_PP_EXPR_IIF_0'

The macro expands correctly.

Perhaps there is a better way to do what I am after.  I would like to 
create a comma separated list (no parenthesis as would be the case if I 
only took the array data) from a possibly empty set.

Thanks,
John