How to find an element in c++23 std::mdspan? Let's say there is some 2D mdspan. How can I find an element and get it's 2D indices?
I guess I can call data_handle() to get an access to underlaying data and do a 1D array search, but this will give me a 1D index. Does mdspan provide a method to map it back to 2D index?
Use std::ranges::find with a custom projection.
#include <vector>
#include <algorithm>
#include <iostream>
#include <ranges>
int main(){
std::vector vec = {1, 2, 3, 4, 5, 6, 7, 88, 9, 10, 11, 12};
auto ms = std::mdspan(vec.data(), 2, 6);
auto coeff_view = std::views::cartesian_product(std::views::iota(0uz, ms.extent(0)),
std::views::iota(0uz, ms.extent(1)));
auto iter = std::ranges::find(coeff_view, 88, [ms](const auto rc){
auto [r,c] = rc;
return ms[r, c];
});
auto [foundr, foundc] = *iter;
std::cout << foundr << "," << foundc << '\n';
}
The above outputs 1,1.