Does GCC have a built-in compile time assert?

Question

Our existing compile-time assert implementation is based on negative array index, and it provides poor diagnostic output on GCC. C++0x's static_assert is a very nice feature, and the diagnostic output it provides is much better. I know GCC has already implemented some C++0x features. Does anyone know if static_assert is among them and if it is then since what GCC version?

Answer 1

According to this page, gcc has had static_assert since 4.3.

Answer 2

If you need to use a GCC version which does not support static_assert you can use:

#include <boost/static_assert.hpp>

BOOST_STATIC_ASSERT( /* assertion */ )

Basically, what boost does is this:

Declare (but don't define!) a

template< bool Condition > struct STATIC_ASSERTION_FAILURE;

Define a specialization for the case that the assertion holds:

template <> struct STATIC_ASSERTION_FAILURE< true > {};

Then you can define STATIC_ASSERT like this:

#define STATIC_ASSERT(Condition) \ 
  enum { dummy = sizeof(STATIC_ASSERTION_FAILURE< (bool)(Condition) > ) }

The trick is that if Condition is false the compiler needs to instantiate the struct

STATIC_ASSERTION_FAILURE< false >

in order to compute its size, and this fails since it is not defined.