variable sized object may not be initialized - c

Question

I am getting the error variable sized object may not be initialized and I don't understand why.
Could someone show me how to fix this line?
int arr[size] = (int *)(augs->one);
Here is my code:
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <pthread.h>
#include <assert.h>
int count = 0;
int cmpfunc(const void *a, const void *b) {
return (*(int*)a - *(int*)b);
}
struct structure {
int two;
int *one;
};
void *sort(void *augments) {
struct structure *augs = (struct structure*)augments;
int i = 0;
int size = 1;
size = augs->two;
int arr[size] = (int *)(augs->one);
//int *arr = (int *)data;
//printf("sizeof:%d\n", sizeof(arr));
qsort(arr, size, sizeof(int), cmpfunc);
printf("finaloutput:\n");
for (i = 0; i < size; i++) {
printf("%d ", arr[i]);
}
printf("\n");
return NULL;
}
int main(int argc, char *argv[]) {
FILE *myFile;
myFile = fopen("data.txt", "r");
// number of lines in file
char charicter;
for (charicter = getc(myFile); charicter != EOF; charicter = getc(myFile)) {
if (charicter == '\n') {
count++;
}
}
printf("count is %d\n", count);
int numberArray[count];
int i = 0;
if ((myFile = fopen("data.txt", "r"))) {
while ((fscanf(myFile, "%d", &numberArray[i]) != EOF)) {
++i;
}
fclose(myFile);
}
assert(argv[1] != NULL);
int num = atoi(argv[1]); //num equals number input
int arrayarray[num - 1][(count / num)];
int idx;
for (i = 0; i < (count); i++) {
printf("numberarray[%d]= %d\n", i, numberArray[i] /*[0],numberArray[i][1]*/);
}
for (i = 1; i < num + 1; i++) {
for (idx = 0; idx < (count / num); idx++) {
arrayarray[i - 1][idx] = numberArray[i * idx];
}
}
///*
for (i = 0; i < ((count / num)); i++) {
printf("arrayarray[0]=%d\n", arrayarray[0][i]);
}
//*/
int lastarray[((count / num) + (count % num))];
for (idx = 0; idx < ((count / num) + (count % num)); idx++) {
lastarray[idx] = numberArray[idx + ((count / num) * (num - 1))];
}
for (i = 0; i < ((((count / num) + (count % num)))); i++) {
printf("lastaray[%d]=%d\n", i, lastarray[i]);
}
//*******************
pthread_t thread_id_arr[num];
for (i = 0; i < num; i++) {
pthread_t tid;
struct structure *augs;
if (i != (num - 1)) {
augs = malloc(sizeof(struct structure) + sizeof(int) + sizeof(int) * num);
(*augs).one = arrayarray[i];
(*augs).two = (count / num);
pthread_create(&tid, NULL, sort, augs);
} else {
(*augs).one = lastarray;
(*augs).two = (count / num) + (count % num);
pthread_create(&tid, NULL, sort, augs);
//pthread_create(&tid, NULL, sort, (void*)lastarray);
}
thread_id_arr[i] = tid;
}
for (i = 0; i < num; i++) {
pthread_join(thread_id_arr[i], NULL);
}
return 0;
}

Answer 1

As others pointed out, you can't initialize a Variable Length Array with a pointer, like you are doing. However, you don't actually need a VLA at all. Use this instead :
int *arr = augs -> one;
You want to act directly on the array that is passed into the thread, not make a copy of it.
That being said, I see another problem. In the loop that spawns the sorting threads, you are not allocating a new args on the last loop iteration, it reuses the allocated args from the previous iteration, which can cause disaster for the 2nd-to-last thread. You need to move the malloc() call above the if.
Also, the malloc() is allocating more memory than your threads actually use. You only need to allocate enough memory for just the struct by itself, not for any integers following the struct.
Also, when each thread is done using the allocated args that it is given, it needs to free() the args to avoid leaking memory.