[ACCEPTED]-Does GCC have a built-in compile time assert?-static-assert
If you need to use a GCC version which does 8 not support static_assert you can use:
#include <boost/static_assert.hpp>
BOOST_STATIC_ASSERT( /* assertion */ )
Basically, what 7 boost does is this:
Declare (but don't define!) a
template< bool Condition > struct STATIC_ASSERTION_FAILURE;
Define 6 a specialization for the case that the assertion 5 holds:
template <> struct STATIC_ASSERTION_FAILURE< true > {};
Then you can define STATIC_ASSERT 4 like this:
#define STATIC_ASSERT(Condition) \
enum { dummy = sizeof(STATIC_ASSERTION_FAILURE< (bool)(Condition) > ) }
The trick is that if Condition 3 is false the compiler needs to instantiate 2 the struct
STATIC_ASSERTION_FAILURE< false >
in order to compute its size, and 1 this fails since it is not defined.
The following code works as expected with 2 g++ 4.4.0 when compiled with the -std=c++0x flag:
int main() {
static_assert( false, "that was false" );
}
it 1 displays:
x.cpp: In function 'int main()':
x.cpp:2: error: static assertion failed: "that was false"
If you have an older gcc or use an older 2 C++ standard, or use C, then you can emulate 1 static_assert as described here: http://www.pixelbeat.org/programming/gcc/static_assert.html
This doesn't really answer the question, but 3 I like compile-time asserts based on switch-case 2 better, e.g.
#define COMPILE_TIME_ASSERT(cond) do { switch(0) { case 0: case cond: ; } } while (0)
Works also in C and not only 1 in C++.
NSPR does:
#define PR_STATIC_ASSERT(condition) \
extern void pr_static_assert(int arg[(condition) ? 1 : -1])
which fails if condition is false because 1 it declares an array of negative length.
you can always play around with templates 4 and non-existant strutures via template-specialization. This 3 is how boost does it as far as I know. This 2 is what I use as a static_assert, it's pretty 1 straight forward.
namespace Internal
{
template<bool x> struct SASSERT_F;
template< > struct SASSERT_F <true> {};
template<int x> struct SASSERT_P {};
#define STATIC_ASSERT(B) \
typedef Internal::SASSERT_P <( \
sizeof (Internal::SASSERT_F <( \
((B)? true : false)) >) \
)> \
StaticAssert##__LINE__ ()
}
Example Of Use
int main(int argc, char **argv)
{
static_assert(sizeof(int) == 1) // Error
static_assert(sizeof(int) == sizeof(int)) // OK
}
Both
BOOST_STATIC_ASSERT(x)
BOOST_STATIC_ASSERT_MSG(x, msg)
will use the C++11 static_assert if 1 your compiler supports it
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