Does GCC have a built-in compile time assert?

If you have an older gcc or use an older C++ standard, or use C, then you can emulate static_assert as described here: http://www.pixelbeat.org/programming/gcc/static_assert.html

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.

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

The following code works as expected with g++ 4.4.0 when compiled with the -std=c++0x flag:

int main() {
    static_assert( false, "that was false" );
}

it displays:

x.cpp: In function 'int main()':
x.cpp:2: error: static assertion failed: "that was false"