how to get 3rd dimension array in 3d array in C++?

Question

int array[3][3][8] = {
    {{3, 4, 5}, {3, 5, 7}, {5, 6, 7}},
    {{1, 3, 5}, {0, 1, 2, 3, 4, 5, 6, 7}, {1, 5, 7}},
    {{1, 2, 3}, {1, 3, 7}, {0, 1, 7}}
};

User inputs x,y coordinate and direction, at that location they can only move in 0-7 direction. However, each location can only move towards certain direction. Therefore I am making this array to see if that direction is in that x, y coordinate’s array. After I get the 3rd dimension array (becomes 1d array), I will see if user input direction is in that array. For example:

 {3,4,5} at 1x1 // then check if direction is in this array

I tried:

 int new_array[8] = array[1][1];

Error: array must be initialized with a brace-enclosed initializer

 int new_array = array[1][1][]; // {3,4,5}

Error: expected primary-expression before ']' token
So I know this syntax isn't valid, are there other ways to achieve such operation? To copy the 3rd dimension array into a new array.

not clear what is the issue. You want copy from your 3d array to some other array? You want to change data from [1,2,3,4,5,6,7,8] to [3,4,5]? What exactly the issue? your first snippet works just fine. — Sugar
– Sugar, Commented Feb 11, 2021 at 17:19
I was trying to copy that 3rd dimension array out then do if in array with a user input value — maxtam642
– maxtam642, Commented Feb 11, 2021 at 17:24
Still unclear. So you set user at {0,0,0} and he inputs something like x=0,y=0, coord=5 meaning we want to change z value at [0][0][5]? Or values inside arrays represent some relation to other array indicies and it's data is some graph? We need some example how do you want to use it — Sugar
– Sugar, Commented Feb 11, 2021 at 17:40

Ted Lyngmo · Accepted Answer · 2021-02-11 18:28:35Z

1

You could use std::copy:

#include <algorithm>
#include <iterator>

//...

    int new_array[8];

    std::copy(std::begin(array[1][1]),
              std::end(array[1][1]),
              new_array);

Done using std::array:

#include <array>

// ...

    std::array<std::array<std::array<int, 8>, 3>, 3> array = {{
        {{
            {3,4,5},
            {3,5,7},
            {5,6,7}
        }},
        {{
            {1,3,5},
            {0,1,2,3,4,5,6,7},
            {1,5,7}
        }},
        {{
            {1,2,3},
            {1,3,7},
            {0,1,7}
        }},
    }};

    std::array<int, 8> new_array = array[1][1];

    // the same result but simpler:

    auto new_array = array[1][1];

edited Feb 11, 2021 at 18:28

answered Feb 11, 2021 at 17:49

Ted Lyngmo

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3 Comments

maxtam642 Over a year ago

Thank you for your answer that’s what I was looking for

Ted Lyngmo Over a year ago

@Mcmx385 You're welcome! You could also take a look at using std::array. If often simplifies things like this.

Ted Lyngmo Over a year ago

@Mcmx385 I added using std::array as an option. It took me some time to get the braces right I must admit. :-)

ΦXocę 웃 Пepeúpa ツ · Accepted Answer · 2021-02-11 17:14:56Z

0

there is no way you can get the col or row of an array like that... if you define a primitive array then you have to navigate the cells and asign the values

int main() {
    int test[2][3][2] = {
                            {
                                {1, 2},
                                {3, 4},
                                {5, 6}
                            }, 
                            {
                                {7, 8}, 
                                {9, 10}, 
                                {11, 12}
                            }
                        };
    int z[2]; 
    for (int i = 0; i < 2; ++i) {
        for (int j = 0; j < 3; ++j) {
            for (int k = 0; k < 2; ++k) {
                z[k] = test[i][j][k];
            }
        }
    }

    for (int k = 0; k < 2; ++k)
    {
        cout << "z[" << k << "] = " << z[k] << endl;
    }
    return 0;

answered Feb 11, 2021 at 17:14

ΦXocę 웃 Пepeúpa ツ

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1 Comment

maxtam642 Over a year ago

Is there another way to define the 3D?

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