Creating an array of pointers to int[]

Hello all,

I am just beginning to learn C, and have been reading K&R. Ive been doing some exercises from the book, and those ive found online. Ive written a binary search algorithm which operates on rotated sorted lists ({0,1,2,3,4,5} -> {3,4,5,1,2,0}), and would like to test my arrays using nested for loops.

For this reason, I am trying to create one array containing pointers to other int arrays. However, I cant seem to do this properly. I am unsure how to declare an array of pointers to int[]. It seeems incorrect to declare it as an 'int *arr' or 'int[] *arr'. Originally, I had tried passing a pointer to the first element of each sub-array (*a instead of (*a)[size]), but it gave me strange results when i printed out the contents of the sub-arrays.

I am trying to understand the language mechanics and the usage of pointers better, so please comment on the code if there is clearly a better way to do something.

Please ignore the function call to rotated_bin_search().

Code:

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/* This short function is used to print out the contents of a
 * specified array.
 */

void printArr(int *arr, int length){
  for(int i = 0; i < length; i++){
    printf("%d ", arr[i]);
  }
  printf("\n");
}

int main(void) {
 
  int *arr,(*a)[ARR_LENGTH], (*b)[ARR_LENGTH], (*c)[ARR_LENGTH], (*d)[ARR_LENGTH], (*e)[ARR_LENGTH], *t; 
  int a_arr[ARR_LENGTH] = {1,2,3,4,5,6,7,8,9,10};
  int b_arr[ARR_LENGTH] = {5,6,7,8,9,10,1,2,3,4};
  int c_arr[ARR_LENGTH] = {6,7,8,9,10,1,2,3,4,5};
  int d_arr[ARR_LENGTH] = {3,4,5,6,7,8,9,10,1,2};
  int e_arr[ARR_LENGTH] = {9,10,1,2,3,4,5,6,7,8};

  a = &a_arr;
  b = &b_arr;
  c = &c_arr;
  d = &d_arr;
  e = &e_arr;

  int *t_arr[5] = {*a, *b, *c, *d, *e};
  //t = &t_arr[0];

  for(int k = 0; k < 5; k++){
    //arr = t + k;
    arr = &t_arr[k];
    printf("\nthe array is:\n");
    printArr(arr, ARR_LENGTH);
    /*for(int j = 0; j < 10; j++){
      int target = j + 1;
      int count = 0;
      int found = rotated_bin_search(arr, ARR_LENGTH, target, &arr[0], &arr[9], count);
      if(found!=0)
        printf ("\n%d was found in the array\n", found);
    }*/
  }

  return 1;
}

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Thanks!

Code:

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int *array[ SIZE ];

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This is an array of pointers to integers.

Code:

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int (*array)[SIZE];

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This is a pointer to an array of integers.

You probably want the former, not the latter. Then you do something like:

Code:

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int array1[ SIZE ] = { ...stuff... };
...
int arrayN[ SIZE ] = { ...stuff... };

int *array[ SIZE ] = { array1, array2, ... arrayN };

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Quzah.

Thanks!

If any other newbies ever have this problem.....

Code:

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int main(void) {
 
  int *arr;
  int a_arr[ARR_LENGTH] = {1,2,3,4,5,6,7,8,9,10};
  int b_arr[ARR_LENGTH] = {5,6,7,8,9,10,1,2,3,4};
  int c_arr[ARR_LENGTH] = {6,7,8,9,10,1,2,3,4,5};
  int d_arr[ARR_LENGTH] = {3,4,5,6,7,8,9,10,1,2};
  int e_arr[ARR_LENGTH] = {9,10,1,2,3,4,5,6,7,8};

  int *t_arr[5] = {a_arr, b_arr, c_arr, d_arr, e_arr};

  for(int k = 0; k < 5; k++){
    arr = t_arr[k];
    printf("\nthe array is:\n");
    printArr(arr, ARR_LENGTH);
    for(int j = 0; j < 10; j++){
      /*int target = j + 1;
      int count = 0;
      int found = rotated_bin_search(arr, ARR_LENGTH, target, &arr[0], &arr[9], count);
      if(found!=0) {
        printf ("%d was found in the array\n", found);
      }*/
    }
  }

  return 1;
}

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