c++ - Compile time sizeof_array without using a macro

Question

This is just something that has bothered me for the last couple of days, I don't think it's possible to solve but I've seen template magic before.

Here goes:

To get the number of elements in a standard C++ array I could use either a macro (1), or a typesafe inline function (2):

(1)

#define sizeof_array(ARRAY) (sizeof(ARRAY)/sizeof(ARRAY[0]))

(2)

template <typename T>
size_t sizeof_array(const T& ARRAY){
    return (sizeof(ARRAY)/sizeof(ARRAY[0]));
}

As you can see, the first one has the problem of being a macro (for the moment I consider that a problem) and the other one has the problem of not being able to get the size of an array at compile time; ie I can't write:

enum ENUM{N=sizeof_array(ARRAY)};

or

BOOST_STATIC_ASSERT(sizeof_array(ARRAY)==10);// Assuming the size 10..

Does anyone know if this can be solved?

Update:

This question was created before constexpr was introduced. Nowadays you can simply use:

template <typename T>
constexpr auto sizeof_array(const T& iarray) {
    return (sizeof(iarray) / sizeof(iarray[0]));
}

Answer 1

Try the following from here:

template <typename T, size_t N>
char ( &_ArraySizeHelper( T (&array)[N] ))[N];
#define mycountof( array ) (sizeof( _ArraySizeHelper( array ) ))

int testarray[10];
enum { testsize = mycountof(testarray) };

void test() {
    printf("The array count is: %d
", testsize);
}

It should print out: "The array count is: 10"