Static assert in C

Question

What\'s the best way to achieve compile time static asserts in C (not C++), with particular emphasis on GCC?

Answer 1

If using the STATIC_ASSERT() macro with __LINE__, it is possible to avoid line number clashes between an entry in a .c file and a different entry in a header file by including __INCLUDE_LEVEL__.

For example :

/* Trickery to create a unique variable name */
#define BOOST_JOIN( X, Y )      BOOST_DO_JOIN( X, Y )
#define BOOST_DO_JOIN( X, Y )   BOOST_DO_JOIN2( X, Y )
#define BOOST_DO_JOIN2( X, Y )  X##Y
#define STATIC_ASSERT(x)        typedef char \
        BOOST_JOIN( BOOST_JOIN(level_,__INCLUDE_LEVEL__), \
                    BOOST_JOIN(_assert_on_line_,__LINE__) ) [(x) ? 1 : -1]