CODEWITHSUNDEEP
cpointers
BigBugNoob
BigBugNoob

Reputation: 41

passing a pointer argument to a function in other file

I'm trying a very basic program...it's about generating an array, returning its pointer and using this pointer in a insertion sort. The fact is main, sort and generate are different files in the program and when use the pointer as argument for the sorting functions I don't have the correct numbers in the pointer. I would appreciate some help!

This is how I generate the pointer...

int
* (generate_matrix) (int number)
{
    srand((unsigned int) time(NULL)); //retirar o null para parar gerar aleatorio
    int array_data[number];
    ptr = (int *) malloc(number*sizeof(int));
    // TODO: comment me
    for (int i = 0; i < number; i++)
    {
        array_data[i] = (rand() % LIMIT);
        printf("%d\n", array_data[i]);
    }
    printf("*****************inside generate array ****************\n");
    ptr = &array_data[0];
    for (int i = 0; i < number; i++)
        printf("%d\n", ptr[i]);
    printf("*****************inside generate ptr ****************\n");
    return ptr;
}

this is how I sort it...

void sort(int ptr[],int number)
{
    printf("before sort:\n");
    printf("number: %d:\n",number);

    for (int i = 0; i < number; i++)
        printf("%d\n", ptr[i]);

    printf("*************\n");

    for (int j=1; j < number; j++)
    {

        int key = ptr [j];
        //printf("%d\n", ptr[j]);
        int i = j - 1 ;
        while (i >= 0 && ptr [i] > key)
        {
            ptr [i + 1] = ptr [i];
            i--;
            ptr [i + 1] = key;
            //printf("%d\n", ptr[i])
        }
    }
    printf("Sorted list in ascending order:\n");

    for (int i = 0; i < number; i++)
        printf("%d\n", ptr[i])
}

follow below the answer by xcode.

65459 28173 10284
*****************inside generate array ****************  65459 28173 10284
*****************inside generate ptr ****************  65459 28173 10284
***************** after paasage to  find ****************  before sort: number: 3  0 0 0
************* Sorted list in ascending order: 0 0 0

Upvotes: 1

Views: 126

Answers (1)

NoDataFound
NoDataFound

Reputation: 11959

That's because you are assigning ptr to a local array, eg: 

int array_data[number]; // <-- the local array
    ptr = (int *) malloc(number*sizeof(int));

And you are losing the content of it:

ptr = &array_data[0];

Which is a memory leak.

So, do :

int* (generate_matrix) (int number) {
  srand((unsigned int) time(NULL)); //retirar o null para parar gerar aleatorio

  int* ptr = (int *) malloc(number*sizeof(int));
  if (NULL == ptr) { // don't forget to check for NULL
    // error
    return NULL;
  }

  for (int i = 0; i < number; i++) {
    ptr[i] = (rand() % LIMIT);
  }
  return ptr;
}

And that's all !

As for the differences between using int* ptr or int ptr[], I don't remember a real reason apart from semantics (eg: int* is a pointer to an int, while int ptr[] is an array of int, but ptr[i] <=> *(ptr + i)).

Upvotes: 2

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