My recovered images don't match in CS50 PSET4 Recover

问题

I'm attempting the 'Recover' question on CS50's pset4.

Though my code produced all 50 pictures, there is a bug as when I ran checkcs50, the first, middle, and 049 image doesn't match.

To be clear, I was able to retrieve 000.jpg, followed immediately by files 002.jpg through 0050.jpg.

Can anyone please tell me what I did wrong in my code? Thank you all very much in advance!

Here's my code:

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

bool magictag(int *);

int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        fprintf(stderr,"Usage:./recover image\n");
        return 1;
    }
    FILE *memorycard = fopen(argv[1], "r");
    if (!memorycard)
    {
        fprintf(stderr, "File cannot be opened\n");
        return 2;
    }

    int file_no = 0;
    int b = 0;
    char a[1000];
    char z[1000];
    //While haven't reached EOF
    while (((b = fread(a, 512, 1, memorycard) != 0)))
    {
        //since fread moved the pointer 512 byte forward
        fseek(memorycard, -512, SEEK_CUR);
        //Check for JPEG Header
        uint8_t c[10];
        fread(c, 1, 4, memorycard);
        fseek(memorycard, -4, SEEK_CUR);
        if ((bool) magictag == true)
        {
            char buffer [50];
            sprintf(buffer, "%03i.jpg", file_no);
            //Open new JPEG file
            FILE *JPEG = fopen(buffer, "w");
            if (!JPEG)
            {
                fprintf(stderr, "jpg cannot be created\n");
                return 3;
            }
            char tmp1[1000];
            fread(tmp1, 512, 1, memorycard);
            fwrite(tmp1, 512, 1, JPEG);
            //copy till a new jpeg is encountered or end of file is reached
            int w = 0;
            char tmp2[1000];
            uint8_t d[10];
            while (((w = fread(z, 4, 1, memorycard) != 0)))
            {
                fseek(memorycard, -4, SEEK_CUR);
                fread(d, 4, 1, memorycard);
                fseek(memorycard, -4, SEEK_CUR);
                if (d[0] == 0xff && d[1] == 0xd8 && d[2] == 0xff && (d[3] & 0xf0) == 0xe0)
                {
                    break;
                }
                if (d[0] != 0xff || d[1] != 0xd8 || d[2] != 0xff || (d[3] & 0xf0) != 0xe0)
                {
                    fread(tmp2, 512, 1, memorycard);
                    fwrite(tmp2, 512, 1, JPEG);
                }
            }
            fclose(JPEG);
            file_no++;
        }
        else
        {
            fseek(memorycard, 512, SEEK_CUR);
        }
    }
    fclose(memorycard);
}

bool magictag(int *c)
{
    if (c[0] == 0xff && c[1] == 0xd8 && c[2] == 0xff && (c[3] & 0xf0) != 0xe0)
    {
        return true;
    }
    else
    {
        return false;
    }
}

来源：https://stackoverflow.com/questions/63453516/my-recovered-images-dont-match-in-cs50-pset4-recover

标签

cs50

recover