Malloc with structs in C

Question

I have a struct:

struct numbers_struct {
char numbers_array[1000];
};

struct numbers_struct numbers[some_size];

After creating struct, there is an integer number as an input:

scanf("%d",&size);

I need to use malloc(size) and specify the size of the array numbers. (instead of some_size use size)

Is something like this possible in C?

Answer 1

Yes it is but malloc() require the total amount of memory require for the array, not the number of elements:

struct numbers_struct* numbers = malloc(size * sizeof(*numbers));
if (numbers)
{
}

Note that you must check the return value of scanf() before using size (which is a poor name in this case) otherwise the code could be using an uninitialized variable if scanf() fails:

int number_of_elements;
if (1 == scanf("%d", &number_of_elements))
{
    struct numbers_struct* numbers =
        malloc(number_of_elements * sizeof(*numbers));
    if (numbers)
    {
        free(numbers); /* Remember to release allocated memory
                          when no longer required. */
    }
}

Variable length arrays were introduced in C99 but there are restrictions around their use (they cannot be used at file scope for example).

Answer 2

May be you can do like this

 struct numbers_struct {
char numbers_array[1000];
};

scanf("%d",&size);

struct numbers_struct *numbers = malloc(sizeof(numbers_struct) * size);