Yeah, I see now. I forgot that even when declaring a parameter in the form 'arr[]' - 'arr' is a pointer. So using sizeof(arr)/sizeof(type) is basically useless if it only works for statically allocated arrays. Could some1 explain:
//CODE
template<class T, size_t N> T decay_array_to_subtype(T (&a)[N]);
#define dimension_of(X) (sizeof(X)/sizeof(decay_array_to_subtype(X)))
How can this give a compile error if X is only a pointer?
Maybe wrapping an array in a new class with a getLength() function could be a good solution?
Finding array length -- C++
Quote:Original post by Cacks
Yeah, I see now. I forgot that even when declaring a parameter in the form 'arr[]' - 'arr' is a pointer. So using sizeof(arr)/sizeof(type) is basically useless if it only works for statically allocated arrays. Could some1 explain:
//CODE
template<class T, size_t N> T decay_array_to_subtype(T (&a)[N]);
#define dimension_of(X) (sizeof(X)/sizeof(decay_array_to_subtype(X)))
How can this give a compile error if X is only a pointer?
Maybe wrapping an array in a new class with a getLength() function could be a good solution?
It gives a compiler error because an array and a pointer are two distinct types.
A pointer is a variable which contains an address of an element of type T (which may or may not exist).
An array is a contiguous block of N elements of type T.
A variable declared to be a T&, that is “reference to type T”, can only be initialized by an object of type T or by an object that can be converted into a T.
There are no available conversions from type T* (pointer to type T) to type T [N] (array of N elements of type T), so the decay_array_to_subtype function cannot compile when called with a pointer.
Quote:Original post by Anonymous Poster
Anyone got one without the "evil" #define? [looksaround]
This works for me.
template < typename T, size_t N > size_t elementsof( T const (&a)[N] ) { return N; } 
Quote:Original post by JohnBolton
This works for me.template < typename T, size_t N > size_t elementsof( T const (&a)[N] ) { return N; }
int a[10]; int b[elementsof(a)]; will not compile, nor can us use elementsof(a) as a template argument.
_countof(x) implementation in Visual Studio is very similar to what's been posted on this thread already; from memory it looks like this:
I remember it well because I could never figure out what is that +0 supposed to be doing.
template <typename T, std::size_t N> char (* helper(T(&)[N]))[N];
#define _countof(x) (sizeof (*helper(x)) + 0)I remember it well because I could never figure out what is that +0 supposed to be doing.
_countof(x) implementation in Visual Studio is very similar to what's been posted on this thread already; from memory it looks like this:
template <typename T, std::size_t N> char (* helper(T(&)[N]))[N];
#define _countof(x) (sizeof (*helper(x)) + 0)
I remember it well because I could never figure out what is that +0 supposed to be doing.
Duuuuude. You just replied to a thread that is almost 7 years old. Welcome to GameDev and all, but necroing is something that the community generally dislikes, FYI. The OP hasn't even logged in since 7 Sep 2009...
This topic is closed to new replies.
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