[Boost.] Multi

Disclosure: This is not an official or accepted Boost library and is unrelated to the std::mdspan proposal. It is in the process of being proposed for inclusion in Boost and it doesn't depend on Boost libraries.

© Alfredo A. Correa, 2018-2025

Multi is a modern C++ library that provides manipulation and access of data in multidimensional arrays for both CPU and GPU memory.

#include <cassert>          // for assert
#include <multi/array.hpp>  // from https://gitlab.com/correaa/boost-multi or https://gitlab.com/correaa/boost-multi

namespace multi = boost::multi;

int main() {
    multi::array<int, 2> A = {{1, 2, 3}, {4, 5, 6}};  // 2D array of integers

    assert(A.size() == 2);                    // the array has 2 rows
    assert(A.size() == A.end() - A.begin());  // interators to rows

    assert(A[1][1] == 5);  // element access through indexing

    assert(A.elements().size() == 2 * 3);  // array has 6 elements
    assert(A.elements()[4] == 5);          // elements gives "flat" sequences
}

(online)

Learn about Multi

• Online documentation

Try Multi

Before installing the library, you can try it online through the Godbolt's Compiler Explorer.

Install Multi

Multi has no external dependencies and can be used immediately after downloading.

git clone https://gitlab.com/correaa/boost-multi.git

Multi doesn't require installation since a single header is enough to use the entire core library;

#include <multi/array.hpp>

int main() { ... }

The library can be also installed with CMake. The header (and CMake) files will be installed in the chosen prefix location (by default, /usr/local/include/multi and /usr/local/share/multi).

cd boost-multi
mkdir -p build && cd build
cmake . -B ./build  # --install-prefix=$HOME/.local
cmake --install ./build  # or sudo ...

Testing the library requires Boost.Core (headers), installed for example, via sudo apt install cmake git g++ libboost-test-dev make or sudo dnf install boost-devel cmake gcc-c++ git. A CMake build system is provided to compile and run basic tests.

ctest -C ./build

Once installed, other CMake projects (targets) can depend on Multi by adding a simple add_subdirectory(my_multi_path) or by find_package:

find_package(multi)  # see https://gitlab.com/correaa/boost-multi

Alternatively, the library can be fetched on demand:

include(FetchContent)
FetchContent_Declare(multi GIT_REPOSITORY https://gitlab.com/correaa/boost-multi.git)
FetchContent_MakeAvailable(multi)
...
target_link_libraries(my_target PUBLIC multi)

Support

• File a Gitlab issue or Github issue.
• Join the #boost-multi discussion group at cpplang.slack.com