C Array Initializer With Different Sizes?

Question

I'm trying to make a multidimensional array, which contains lots of data.

However, I don't know the initializer size of the middle array since this is always different for each array level.

It looks like this:

 char* spawnableVehicles[3][][3] = {
      {
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
      },
      {
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
      },
      {
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
      },
 }

How do I initialize the size of the middle array?

You cannot have an array of arrays that are different sizes. Each element of an array must be the same type, including size. (spawnableVehicles[0] cannot be an array of five things while spawnableVehicles[1] is an array of three things.) You must either specify a maximum size for the middle dimension that encompasses all cases, or you must use a different data structure. — Eric Postpischil
– Eric Postpischil, Commented Jan 6, 2019 at 16:02
You can't have a different size for any inner array. They all must be the same size. So, choose an appropriate maximum and use that: char* spawnableVehicles[3][8][3] ... or stop using your array approach and switch to pointers with malloc() and free(). — pmg
– pmg, Commented Jan 6, 2019 at 16:06
@EricPostpischil Okay, clear. What would be a appropriate data structure for my case? — Appel Flap
– Appel Flap, Commented Jan 6, 2019 at 16:07
@AppelFlap: Your question does not state much about the situation. An array of pointers to arrays might be suitable, with each pointer being set to an address returned by malloc. — Eric Postpischil
– Eric Postpischil, Commented Jan 6, 2019 at 16:21

Mostafa Ayaz · Accepted Answer · 2019-01-06 16:34:47Z

2

You need to identify all the indices clearly. The definition as spawnableVehicles[3][][3] yields to error while when I defined spawnableVehicles[30][30][30] the error vanished. I also wrote a code to check this out:

#include<iostream>
using namespace std;
int main(){
    char* spawnableVehicles[30][30][30] = {
      {
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
      },
      {
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
      },
      {
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
           {"test1", "test2", "test3"},
      },
 };
 for (int i=0;i<30;i++){
    for (int j=0;j<30;j++){
        for (int k=0;k<30;k++){
            if (spawnableVehicles[i][j][k]!=NULL){
                // printing spawnableVehicles[i][j][k] when it has a value other than NULL
                cout<<i<<"   "<<j<<"   "<<k<<"   "<<spawnableVehicles[i][j][k]<<"\n";
            }
        }
    }
 }
 return 0;
}

with the following result:

0   0   0   test1
0   0   1   test2
0   0   2   test3
0   1   0   test1
0   1   1   test2
0   1   2   test3
0   2   0   test1
0   2   1   test2
0   2   2   test3
0   3   0   test1
0   3   1   test2
0   3   2   test3
0   4   0   test1
0   4   1   test2
0   4   2   test3
1   0   0   test1
1   0   1   test2
1   0   2   test3
1   1   0   test1
1   1   1   test2
1   1   2   test3
1   2   0   test1
1   2   1   test2
1   2   2   test3
2   0   0   test1
2   0   1   test2
2   0   2   test3
2   1   0   test1
2   1   1   test2
2   1   2   test3
2   2   0   test1
2   2   1   test2
2   2   2   test3
2   3   0   test1
2   3   1   test2
2   3   2   test3
2   4   0   test1
2   4   1   test2
2   4   2   test3
2   5   0   test1
2   5   1   test2
2   5   2   test3
2   6   0   test1
2   6   1   test2
2   6   2   test3
2   7   0   test1
2   7   1   test2
2   7   2   test3

--------------------------------
Process exited after 0.08576 seconds with return value 0
Press any key to continue . . .

answered Jan 6, 2019 at 16:34

Mostafa Ayaz

4781 gold badge7 silver badges16 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Appel Flap Over a year ago

Seems to be suitable for my situation. Just a question, how come on the second line it jumps from 4 to 0 again?

Mostafa Ayaz Over a year ago

Well, in which case you mean? I don't see any 4 to 0 in the second line. Or I misunderstood you...

Mostafa Ayaz Over a year ago

This is because of the priority of increments in values of i,j,k. Note that first of all, k increases. When no more increment is possible (say, spawnableVehicles[i][j][k] is NULL) the increment happens next in j similarly after that in i. That's why we have a transition from [0 4 2] to [1 0 0] because for all the vectors [i][j][k] with i=0, j>=4 and k>3 we have spawnableVehicles[i][j][k]=0 and the next immediate non-NULL spawnableVehicles[i][j][k] is spawnableVehicles[1][0][0]

Appel Flap Over a year ago

I appreciate the answer. Thanks!

Collectives™ on Stack Overflow

C Array Initializer With Different Sizes?

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related