#include <stdio.h>
#include <stdlib.h>

int *getinp(const char *filename);


int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <file>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    int *foo = getinp(argv[1]);
    return 0;
}

int *getinp(const char *filename) {
    FILE *fd = fopen(filename, "r");
    if (fd == NULL) {
        fprintf(stderr, "Couldn't open %s for reading\n", filename);
        exit(EXIT_FAILURE);
    }

    int pos = 0;
    int size = 64;
    int *arr = malloc(size * sizeof(int));
    if (arr == NULL) {
        fprintf(stderr, "Not enough memory\n");
        exit(EXIT_FAILURE);
    }
    char c;

    while ((c = fgetc(fd)) != EOF) {
        arr[pos] = c;
        pos++;
        if (pos >= (size - 1)) {
            size *= 2;
            if (realloc(arr, size * sizeof(int)) == NULL) {
                fprintf(stderr, "Not enough memory\n");
                exit(EXIT_FAILURE);
            }
        }
    }
    arr[pos] = '\0';
    fclose(fd);
    return arr;
}

$ gdb --args ./a.out big.bad.testfile
[gdb]> run
Starting program: /home/user/a.out big.bad.testfile

Program received signal SIGSEGV, Segmentation fault.
0x08048646 in getinp (filename=0xbf9c75b1 "big.bad.testfile") at fail.c:34
34              arr[pos] = c;
[gdb]> p size
$1 = 65536
[gdb]> p pos
$2 = 33700
[gdb]> p arr[pos-1]
$3 = 9
[gdb]> p arr[pos]
Cannot access memory at address 0x806b000

size *= 2;
if (realloc(arr, size * sizeof(int)) == NULL) {
   fprintf(stderr, "Not enough memory\n");
   exit(EXIT_FAILURE);
}

size *= 2;
arr = realloc(arr, size * sizeof(int));
if (arr == NULL) {
    fprintf(stderr, "Not enough memory\n");
    exit(EXIT_FAILURE);
}