Initialize multiple dimension array

Question

How can I initialize array with variables like int x[row][col];

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

i want to initialize array as this =

int myarray({2,3,4},{12,4,5},{2,2,2})

in `int x[row][col]` the dimesnions `row` and `col` must be compile time constants, hence you already included the answer in the quesiton and it is not clear what you are asking for — 463035818_is_not_an_ai, Jun 26 '20 at 13:27
perhaps: [Why aren't variable-length arrays part of the C++ standard?](https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard) — 463035818_is_not_an_ai, Jun 26 '20 at 13:28
i mean i dont want to type row and col count when i initializnig the array, so think about a method of class is : vektor ({1,2,3],{2,3,4}) will generate a vektor without typing its row col count — hipativ414, Jun 26 '20 at 13:30
did you encounter any problem when you tried `int myArray[][] = { {1,2,3,4}, ....` ? — 463035818_is_not_an_ai, Jun 26 '20 at 13:33
@idclev463035818 That [doesn't work](https://godbolt.org/z/2LVCCm). Only one dimension can be unspecified. — François Andrieux, Jun 26 '20 at 13:36
@molbdnilo hum... I am trying to find out what is OPs problem.... — 463035818_is_not_an_ai, Jun 26 '20 at 13:36
Implicit instantiation of undefined template 'std::__1::vector >, std::__1::allocator > > >' — hipativ414, Jun 26 '20 at 13:46
and also how can it print like { 1,2,3 } rather then integers and spaces — hipativ414, Jun 26 '20 at 13:48
@hipativ414, post your code, and the errors in the question, this game of trying to guess what you are doing is not a very effective way to solve your problem. — anastaciu, Jun 26 '20 at 13:52
Did you see what @FrançoisAndrieux wrote: "_Only one dimension can be unspecified_"? — Ted Lyngmo, Jun 26 '20 at 14:01
That syntax is not allowed. I think you just have to specify the size of the bounds. You can skip the first one though (`7` in this case). — cigien, Jun 26 '20 at 14:02

score 1 · Accepted Answer · answered Jun 26 '20 at 14:14

The exact answer is you cannot initialize an array like that, i.e., without providing both row and col at compile time, though std::vector can do the job for you.

You can use some code like this:

#include <iostream>
#include <vector>

void print_vector(std::vector<int> &v) {
    std::cout << "{ ";
    for (auto &&i : v) {
        std::cout << i;
        if (&i != &v.back()) {
            std::cout << ",";
        }
    }
    std::cout << " }";
}

void print_matrix(std::vector<std::vector<int>> &v) {
    std::cout << "{ ";
    for (auto &&i : v) {
        print_vector(i);
        if (&i != &v.back()) {
            std::cout << ", ";
        }
    }
    std::cout << " }" << std::endl;
}

int main() {
    std::vector<std::vector<int>> v = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}}; 
// same as std::vector<std::vector<int>> v({{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}});
    print_matrix(v);
// prints { { 1,2,3,4 }, { 5,6,7,8 }, { 9,10,11,12 } } on stdout
}

I have included print_vector and print_matrix since the OP asked about them in the comments, though without thinking much about them. You can get better implementations on this thread.

Initialize multiple dimension array

1 Answers1