Understanding Array of pointers

Question

I am doing something like this;

int main()
{
    int *b[2], j;
    for (j = 0; j < 2; j++)
    {
        b[j] = (int *)malloc(12 * sizeof(int));
    } 
    return 0;
}

Please tell me what this instruction really means? And how can I pass this array of pointers to a function to access values like *(B[0]+1),*(B[1]+1) etc?

Don't [cast the result of malloc](https://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc) — Cid, Jan 14 '20 at 13:46
*Please tell me what this instruction really means?* which one ? — Cid, Jan 14 '20 at 13:46
You are asking someone to explain your code to you? What have you tried to pass an array of pointers? — Scott Hunter, Jan 14 '20 at 13:47
*"And how can I pass this array of pointers to a function"* -> `MyFunction(b);` — Cid, Jan 14 '20 at 13:47
*"how can I pass this array of pointers to a function"* - the same way you pass an array of *anything* to a function. Declare the formal parameter as a pointer to base-type (here, it is `int **`) and pass the array id as the argument from the caller. — WhozCraig, Jan 14 '20 at 14:03
I want to know what malloc function is doing there? Yes, I want someone to explain my code. That in what manner malloc will allocate memory after declaring array of two integer arrays. — Hritikesh Semwal, Jan 14 '20 at 15:43

score 2 · Answer 1 · edited Jan 14 '20 at 16:35

2

int main(void)
{
    int *b[2], j; // initialization of an array of pointers to integers (size = 2)
    for (j = 0; j < 2; j++) // for each of the pointers 
    {
        b[j] = malloc(12 * sizeof (int)); // allocate some space = 12 times size of integer in bytes (usually 4)
    } 
    return 0;
}

If you want to pass this array to a function you can just pass b

foo(b);

edited Jan 14 '20 at 16:35

Toby Speight

27,591
48
66
103

answered Jan 14 '20 at 13:54

Sinking

95
8

4

"size = 2" might be misleading; `sizeof b` would not yield 2. Perhaps "length" would be better, or just "an array of two pointers to `int`." – ad absurdum Jan 14 '20 at 13:59
2

Mentioning what will be the prototype of foo() will add more value to your answer. – MayurK Jan 14 '20 at 14:21

Understanding Array of pointers

1 Answers1