problems with pointer in function

Question

I encountered erratic behavior when initializing array in function.

I have an uninitialized pointer below:

int *arr;

And I am passing it to a function for initialization.

init_arr(&arr);

void init_arr(int **arr)
{
*arr = (int *) calloc(10, sizeof **arr);
}

The pointer is initilized, and when I try get items *arr[2] and larger I get the error:

Cannot access memory to address 0x0

The source code was compiled using gcc version 4.8.4

Try (*arr)[2] and this works! thanks! I need to be careful. Thanks again! — Lakeev Roman
– Lakeev Roman, Commented Oct 25, 2015 at 23:57
I am not sure, but believe (*arr)[2] is equivalent to just arr[2], as the compiler treats a pointer as an array. — Paul Ogilvie
– Paul Ogilvie, Commented Oct 26, 2015 at 0:00
do not cast the returned value from calloc() why? because 1) the returned value is a defined as void * so can be assigned to any other pointer. 2) the cast just clutters the code and can create a real headache when debugging or maintaining the code. — user3629249
– user3629249, Commented Oct 26, 2015 at 0:43

Vlad from Moscow · Accepted Answer · 2015-10-26 00:03:24Z

1

Instead of expression

 *arr[2]

you have to use

 arr[2]

You allocated an array of 10 integers. So to acces an element of the array it is enough to write for example arr[2].

If you mean an access of an element of the allocated array inside the function init then you have to write

 ( *arr )[2]

answered Oct 26, 2015 at 0:03

Vlad from Moscow

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