Equivalents to MSVC's _countof in other compilers?
Using C++11, the non-macro form is:
char arrname[5];size_t count = std::extent< decltype( arrname ) >::value;
And extent
can be found in the type_traits
header.
Or if you want it to look a bit nicer, wrap it in this:
template < typename T, size_t N >size_t countof( T ( & arr )[ N ] ){ return std::extent< T[ N ] >::value;}
And then it becomes:
char arrname[5];size_t count = countof( arrname );char arrtwo[5][6];size_t count_fst_dim = countof( arrtwo ); // 5size_t count_snd_dim = countof( arrtwo[0] ); // 6
Edit: I just noticed the "C" flag rather than "C++". So if you're here for C, please kindly ignore this post. Thanks.
Update: C++ 17 support std::size()
(defined in header <iterator>
)
You can use boost::size()
instead:
#include <boost/range.hpp>int my_array[10];boost::size(my_array);
I'm not aware of one for GCC, but Linux uses GCC's __builtin_types_compatible_p
builtin to make their ARRAY_SIZE()
macro safer (it'll cause a build break if applied to a pointer):
/* &a[0] degrades to a pointer: a different type from an array */#define __must_be_array(a) \ BUILD_BUG_ON_ZERO(__builtin_types_compatible_p(typeof(a), typeof(&a[0])))#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
Note: I think the BUILD_BUG_ON_ZERO()
macro has a misleading name (it causes a build failure if the expression is not zero and returns 0
otherwise):
/* Force a compilation error if condition is true, but also produce a result (of value 0 and type size_t), so the expression can be used e.g. in a structure initializer (or where-ever else comma expressions aren't permitted). */#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
I think the naming for this macro comes from looking at it in two parts: BUILD_BUG_ON
is what the macro does when the expression is true, and ZERO
is the value 'returned' by the macro (if there's not a build break).