Passing boost::multi_array between functions (c++)

Question

Suppose i need a five-dimensional array as class member and want to use it in different functions. For this puropose I use boost::multi_array eg:

class myClass {

typedef boost::multiarray<double, 5> fiveDim;
typedef fiveDim:: index index;

void init(){
fiveDim myArray(boost::extents[3][3][3][3][3]);
// I can use myArray in this scope
}

void printArray(){
// myArray not available here
}

Now, because of the function scope, i can clearly not use myArray in printArray(), but i also can't initialize the array directly in the class scope, outside a function (after the two typedefs.)

How do i define the array so that every class function is able to use it? The dimensions are known at compile time and always the same.

Answer 1

Maybe you can use this:

#include <iostream>
#include <string>
#include <boost/multi_array.hpp>
#include <boost/array.hpp>
#include <boost/cstdlib.hpp>

namespace{
    constexpr size_t dim1_size = 3;
    constexpr size_t dim2_size = 3;
    constexpr size_t dim3_size = 3;
    constexpr size_t dim4_size = 3;
    constexpr size_t dim5_size = 3;
    
    void print(std::ostream& os, const boost::multi_array<double, 5>& a){
        os<<"implementation of print: "<<a[0][0][0][0][0]<<std::endl;
    }
    
    boost::multi_array<double, 5> createArray(){
        return boost::multi_array<double, 5>(boost::extents[dim1_size][dim2_size][dim3_size][dim4_size][dim5_size]);
    }
}

class myClass {

public:
    boost::multi_array<double, 5> myArray = createArray();

    void printArray(){
        print(std::cout, myArray);
    }
};

int main()
{
  myClass a;
  a.myArray[0][0][0][0][0] = 42;
  a.printArray();
}

To pass a boost::multi_array in a function you can use references like in print . To create a boost::multi_array you must return it as copy. The compiler may optimize it to a move.