A problem in C++ primer, when begin and end work on vector I know there is vector::size() could help, but how do they work when I just give an array argument. just like:
int arr[] = {1, 2, 3};
size = end(arr) - begin(arr);
how do end(arr) and begin(arr) work correctly ?
So to see how std::end works we can look at How does std::end know the end of an array? and see that the signature for std::end is:
template< class T, std::size_t N >
T* end( T (&array)[N] );
and it is using template non-type parameter to deduce the size of the array and it is just a matter of pointer arithmetic to obtain the end:
return array + N ;
For std::begin the signature is identical, with the exception of the name:
template< class T, std::size_t N >
T* begin( T (&array)[N] );
and calculating the beginning of the array is simply a matter of array to pointer decay which gives us a pointer to the first element of the array.
In C++14 these both become constexpr.
I'll just paste a piece of code from here
template <class _Tp, size_t _Np>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
_Tp*
begin(_Tp (&__array)[_Np])
{
return __array;
}
template <class _Tp, size_t _Np>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
_Tp*
end(_Tp (&__array)[_Np])
{
return __array + _Np;
}
