Is there a way to pass 2D array or matrix into the c++ code straight from Julia?

[GlockPL]

I managed to pass 1D flatten vector like that:
jlcxx::Array<int> run_heuristic(const std::vector<double>& matrix, std::size_t rows, std::size_t cols)
with julia code looking like that:
solution = run_heuristic(CxxWrap.StdVector(vec_array), size(arr, 1), size(arr, 2))
but this is undesirable, is there a way to that with 2D vector or some other array?

[biona001]

I'm trying to do the same thing. Just want to pass a matrix into C++ and return the sum back to Julia. Somehow it's proven to be difficult and the examples in test is a bit hard to decipher.

@barche do you have any example, or know of any resources that could facilitate this? Thank you in advance.

[barche]

You can use jlcxx::ArrayRef<double, 2> as an argument on the C++ side, and then on the Julia side you can pass a 2D array. See the check_mutable_array function in the containers example for an example.

[biona001]

Thank you, Bart.

For future reference, here's my code to pass a matrix of Float64 into C++, sum them, then get the result back.

Here's my sumarray.cpp file:

#include "jlcxx/jlcxx.hpp"
#include <vector>
#include <iostream>
using namespace std;

double cpp_mat_sum(jlcxx::ArrayRef<double, 2> x) {
    cout << &x[0] << endl; // print memory address of x
    double total = 0;
    for(auto xij : x) {
        total += xij;
    }
    return total;
}

JLCXX_MODULE define_julia_module(jlcxx::Module& mod)
{
    mod.method("cpp_mat_sum", &cpp_mat_sum);
}

And here's my CMakeList.txt

project(Examples)

cmake_minimum_required(VERSION 3.5)
set(CMAKE_MACOSX_RPATH 1)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/lib")

find_package(JlCxx)
get_target_property(JlCxx_location JlCxx::cxxwrap_julia LOCATION)
get_filename_component(JlCxx_location ${JlCxx_location} DIRECTORY)
set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib;${JlCxx_location}")

message(STATUS "Found JlCxx at ${JlCxx_location}")

add_library(hello SHARED hello.cpp)
add_library(sumarray SHARED sumarray.cpp)

target_link_libraries(hello JlCxx::cxxwrap_julia)
target_link_libraries(sumarray JlCxx::cxxwrap_julia)

install(TARGETS
  sumarray 
LIBRARY DESTINATION lib
ARCHIVE DESTINATION lib
RUNTIME DESTINATION lib)

I put them in the same directory, and compile them with:

mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_PREFIX_PATH=/home/groups/sabatti/.julia/dev/libcxxwrap_julia_jll/override /home/users/bbchu/ghostbasilwrap
cmake --build . --config Release

Usage in Julia:

julia> module CppSumArray
       using CxxWrap
       @wrapmodule("/home/users/bbchu/ghostbasilwrap/build/lib/libsumarray")

       function __init__()
           @initcxx
       end
       end

Main.CppSumArray

julia> x = randn(10000, 10000);

julia> CppSumArray.cpp_mat_sum(x)
0x7feb5e860040
-9305.980886268122

julia> sum(x)
-9305.98088626438

julia> pointer(x)
Ptr{Float64} @0x00007feb5e860040

So we are getting the same result, and the matrix in Julia and C++ have the same address.