Given a builtin array x of arbitrary type T, there are functions std::begin() and std::end() that I can call, but why isn't there a std::size()? Seems odd not to have that.
I could use std::end(x)-std::begin(x), but still a std::size(x) would be better.
Yes, I know of the std::vector and std::array classes. This is just a question of why something as simple as this isn't available as yet in the STL.
Just a note to let people know that N4280 "Non-member size() and more (Revision 2)" has been accepted into the C++17 Working Draft. This includes std::size() as well as std::empty() and std::data().
template <class T, size_t N> constexpr bool empty(const T (&array)[N]) noexcept; return only false? N could be zero.
int ar[0]; would not compile.
int ar[] = {};?There's std::extent, which is to be applied to the type of the array:
#include <type_traits>
int a[12];
assert(std::extent<decltype(a)>::value == 12);
Alternatively you can use std::distance(std::begin(a), std::end(a)).
The former is manifestly a constant expression, though in practice the latter can be comuted statically as well.
Finally, there's always the homegrown solution:
template <typename T, std::size_t N>
constexpr std::size_t array_size(T const (&)[N])
{ return N; };
std::extent method.
std::size() would be useful if one wanted to declare multiple arrays of the same length in which the length of the first was determined via list-initialization.c++11 :-)STL algorithm works on iterators, not on any container, size of a STL container would need a start and end, that won't make sense. For such we already have std::distance
int x[] = {1,2,3,4,5}; for_each(std::begin(x), std::end(x), [](int element) { std::cout << element << std::endl; }); Which shows it can use STL algorithms.for (int element : x) std::cout << element << std::endl;?
std::begin(x) is equivalent to std::vector y; y.begin().I suppose you mean C-like arrays. The answer, as Bjarne Stroustrup said, is because "An array in C is a data type that is so stupid that it didn't even know how many elements it got." Once an array decays to a pointer there is no way to know how many elements where there in the 'array'.
std::begin and std::end do).
std::sizeonly work for a type if it is cheap, or should it work regardless?std::begin()andstd::end()?std::valarray::begin. The only container for which you can't add such a member isT[].