CS50 PSET 4 Recover Segmentation fault (core dumped)

Question

I am working on PSET4 Recover from the CS50 course, but I can't seem to get it to work. I keep getting segmentation fault (core dumped). I've tried changing my code many times, but keep the segmentation fault. Can you spot where I go wrong? Thanks!

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <cs50.h>

typedef uint8_t BYTE;
const int FAT_SIZE = 512;

int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        printf("Usage: ./recover image");
        return 1;
    }
    FILE *card = fopen(argv[1], "r");
    if (card == NULL)
    {
        printf("Could not open file.\n");
        return 1;
    }

    int n = 0;
    string filename = "XXX.jpg";
    BYTE temp[FAT_SIZE];
    while (fread(temp, sizeof(BYTE), FAT_SIZE, card) == FAT_SIZE)
    {
        if(temp[0] == 0xff && temp[1] == 0xd8 && temp[2] == 0xff && (temp[3] & 0xf0) == 0xe0)
        {
            newfile:
            sprintf(filename, "%03i.jpg", n);
            FILE *output = fopen(filename, "w");
            if (output == NULL)
            {
                fclose(card);
                printf("Could not create new file.\n");
                return 1;
            }
            fwrite(temp, sizeof(BYTE), FAT_SIZE, output);
            while (fread(temp, sizeof(BYTE), FAT_SIZE, card) == FAT_SIZE)
            {
                if(temp[0] == 0xff && temp[1] == 0xd8 && temp[2] == 0xff && (temp[3] & 0xf0) == 0xe0)
                {
                    fclose(output);
                    n++;
                    goto newfile;
                }
                fwrite(temp, sizeof(BYTE), FAT_SIZE, output);
            }
            fclose(output);
            fclose(card);
            return 0;
        }
    }
}

Answer 1

Ah, finally. I changed the string type for the filename to a char array of 8, and then it works. That was all.