Let's say I have an array of integers defined like that:
static constexpr int IntArray[] = {1, 5, 10, 12, 17};
Is there a way to get the minimum or maximum value at compile time?
1 Answer
Let's get the C++17 solution out of the way for future search-landers:
constexpr int IntArray[] = {1, 5, 10, 12, 17};
constexpr int min = *std::min_element(std::begin(IntArray), std::end(IntArray));
static_assert(min == 1);
C++11 is more picky with constexpr functions, so we have to roll out a recursive algorithm. This one is a simple, linear one:
template <class T>
constexpr T &constexpr_min(T &a, T &b) {
return a > b ? b : a;
}
template <class T>
constexpr T &arrayMin_impl(T *begin, T *end) {
return begin + 1 == end
? *begin
: constexpr_min(*begin, arrayMin_impl(begin + 1, end));
}
template <class T, std::size_t N>
constexpr T &arrayMin(T(&arr)[N]) {
return arrayMin_impl(arr, arr + N);
}
constexpr int IntArray[] = {1, 5, 10, 12, 17};
constexpr int min = arrayMin(IntArray);
11 Comments
Hayt
Here I am manually trying to implement a c++17 version and there i already one. :( But good to know. ;)
AndyG
This doesn't technically answer OPs question because you used a
constexpr and not a static const
Quentin
@AndyG I assumed that it is an oversight. A
const array's contents are not compile-time constants, so if it isn't actually constexpr, nothing can be done at compile-time at all.AndyG
@Quentin: I wouldn't assume anything haha :-) I think the real answer is your second statement "Nothing can be done at compile-time at all"
Kyle Strand
@AndyG ...and would you then recommend not including the info about the
constexpr case, which is actually useful? |
constexprfunctions.