Preview: C++23 mdspan

C++23 introduces mdspan, a multidimensional view into a contiguous memory space. It also allows us to use the , operator in subscripts. This allows us to more easily create a multidimensional array. Here’s an example:

Listing 61 mdspan.cpp

#include <iostream>
#include <vector>
#include <mdspan>

int main() {

    // create a vector with 12 elements
    std::vector<double> _v(12, 0.0);

    // create a 2-d view (4 rows x 3 columns) into it
    auto M = std::mdspan(_v.data(), 4, 3);

    // loop over rows and columns and fill the matrix
    for (std::size_t i = 0; i < M.extent(0); ++i) {
        for (std::size_t j = 0; j < M.extent(1); ++j) {
            M[i, j] = static_cast<double>(100*i + j);
        }
    }

    // output
    for (std::size_t i = 0; i < M.extent(0); ++i) {
        for (std::size_t j = 0; j < M.extent(1); ++j) {
            std::cout << M[i, j] << " ";
        }
        std::cout << std::endl;
    }

}

Note

You need a very recent compiler for this to work. I am using LLVM/clang++ 17 and build as:

clang++ -std=c++23 -stdlib=libc++ -o mdspan mdspan.cpp

On my machine (Fedora 39), I needed to install the libcxx and libcxx-devel packages to get everything I need.

Tip

You can see the status of C++23 support here: compiler / library support for C++23