CODEWITHSUNDEEP
carrayspointers
user8720643
user8720643

Reputation:

Print array that was set in another function with pointers

As you can see in the code below I tried to print an array that I created in a different function. The output was totally different numbers compares to what I expected: numbers between 0 - 20 were set but I got some negative values.

So my question is why is this happening? And how to fix it if it even possible?

#include <stdio.h>
#include <time.h>
#define LEN 10
int* creatingArray();
void printingArray(int* array);
int main(void)
{
    int* pointer_array = creatingArray();
    printingArray(pointer_array);
    getchar();  
    return 0;
}
int* creatingArray()
{
    srand(time(NULL));
    int array[LEN] = { 0 };
    int* i = 0;
    for (i = array; i < array + LEN; i++)
    {
        *i = rand() % 20;
    }
    return array;
}
void printingArray(int* array)
{
    int* i = 0;
    for (i = array; i < array + LEN; i++)
    {
        printf("\n%d\n", *i);
    }
}

Upvotes: 0

Views: 87

Answers (1)

Criticize SE actions means ban
Criticize SE actions means ban

Reputation: 58848

Pay attention to this code:

int* creatingArray()
{
    // stuff
    int array[LEN] = { 0 };
    // more stuff
    return array;
}

array is a local variable, so it gets destroyed when the function returns. You then have a pointer to a destroyed variable. The space where it was will (most likely) continue to hold the data you put there - until the memory gets reused for something else and overwritten.

and how to fix it if it eve/n possible?

Several options:

  1. Make array a static variable. Then it will not be destroyed when the function returns. (This also means that every time you call creatingArray it will use the same array, instead of a new one)

  2. Make array global.

  3. Move array to main, and pass a pointer to it into creatingArray, instead of having creatingArray return one. Then, since it's a local variable in main, it will only be destroyed when main returns.

  4. Use malloc to allocate some space that will not be cleaned up automatically when the function returns.

Upvotes: 1

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