Initializing a pointer to an array of integers.

Question

I have the following problem: I need to initialize a stuct Number that represents a number, for this it needs to contains its value, amount of divisors and the divisors themself. To store the divisors I need to use a pointer to an array of integers, and this is where the problem starts.

 typedef struct {
        int value;
        int divisor_amount;
        int (*divisors)[];
    } Number;

Now since I do not know in advance how many divisors my number posseses I cannot give a length to the array.

In the main function I assign each of these fields a value. For the first two variables this is no problem.

Number six;
six.value = 6;
six.divisor_amount = 3;

Now for the pointer I do not really know how to initialize it. During class it was told to do this as:

six.divisors[0] = 1;
six.divisors[1] = 2;
six.divisors[2] = 3;

but then I get this erroy from the compiler:

[Error] invalid use of array with unspecified bounds

So I thought maybe I needed to assign some space and tried:

six.divisors = malloc(six.divisor_amount*sizeof(int));

But that gives me just another error:

[Warning] assignment from incompatible pointer type [enabled by default]

int (*divisors)[]; is probably not what you want to have. If you want to have a pointer to an array just write int *divisors; and then malloc it during initialisation — UnholySheep
– UnholySheep, Commented Oct 18, 2014 at 12:56
I cannot reproduce the warning. As six.divisors is a (non-function) pointer type, this should actually work. The error message for the first snippet is the same as gcc -std=c99 gives, but I don't get the second one. How do you compile? — mafso
– mafso, Commented Oct 18, 2014 at 17:10

Jens Gustedt · Accepted Answer · 2014-10-18 15:20:04Z

3

int (*divisors)[];

is wrong this is a pointer to array of int.

use

int *divisors;

with this your malloc allocation should work.

edited Oct 18, 2014 at 15:20

answered Oct 18, 2014 at 12:56

Jens Gustedt

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