how to return multi values from function in Armadillo?

Question

I'm new to c++ and Armadillo. I've written a function as follows:

mat solver(mat charge)
{
    mat x = regspace(0, mesh_num - 1);
    mat xx = reshape(x, 1, mesh_num);
    mat xxx = repmat(xx, mesh_num, 1);
    mat y = regspace(0, mesh_num - 1);
    mat yy = reshape(y, mesh_num, 1);
    mat yyy = repmat(yy, 1, mesh_num);
    mat green_func = -0.5 * log(square(step_xc * xxx) + square(step_yc * yyy));
    green_func(0, 0) = 0;
    mat temp_1 = fliplr(green_func);
    mat temp_2 = temp_1.cols(0, mesh_num - 2);
    mat temp_3 = flipud(green_func);
    mat temp_4 = temp_3.rows(0, mesh_num - 2);
    mat temp_5 = fliplr(temp_4);
    mat temp_6 = temp_5.cols(0, mesh_num - 2);
    mat temp_7 = join_horiz(temp_6, temp_4);
    mat temp_8 = join_horiz(temp_2, green_func);
    mat green_fun_expand = join_vert(temp_7, temp_8);
    return green_fun_expand;
}

I'd like to return more-than-one matrix, e.g. green_func_expand and temp_8. How to achieve this?

Answer 1

use a Tuple STL

tuple <mat, mat>  solver(mat charge)
{
    mat x = regspace(0, mesh_num - 1);
    mat xx = reshape(x, 1, mesh_num);
    mat xxx = repmat(xx, mesh_num, 1);
    mat y = regspace(0, mesh_num - 1);
    mat yy = reshape(y, mesh_num, 1);
    mat yyy = repmat(yy, 1, mesh_num);
    mat green_func = -0.5 * log(square(step_xc * xxx) + square(step_yc * yyy));
    green_func(0, 0) = 0;
    mat temp_1 = fliplr(green_func);
    mat temp_2 = temp_1.cols(0, mesh_num - 2);
    mat temp_3 = flipud(green_func);
    mat temp_4 = temp_3.rows(0, mesh_num - 2);
    mat temp_5 = fliplr(temp_4);
    mat temp_6 = temp_5.cols(0, mesh_num - 2);
    mat temp_7 = join_horiz(temp_6, temp_4);
    mat temp_8 = join_horiz(temp_2, green_func);
    mat green_fun_expand = join_vert(temp_7, temp_8);
    return make_tuple( green_fun_expand,temp_8 ) ;
}

while recieving this , try

  mat ret1, ret2;
    tie(ret1, ret2) = solver(mat, change);

then you can directly use ret1 and ret2

Alternatively , you can use a class and add whatever you want to return as class variables, create object of class inside your function, populate the variables and return the object