CS50 pset4 - "Recover"

recover.c

/**
 * recover.c
 *
 * Computer Science 50
 * Problem Set 4
 *
 * Recovers JPEGs from a forensic image.
 */

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

#define BUFFER_SIZE 512

int main(void)
{
    // open memory card file
    FILE* input = fopen("card.raw", "r");
    if (input == NULL)
    {
        printf("Could not open card.raw.\n");
        return 2;
    }
    
    // create buffer
    unsigned char buffer[BUFFER_SIZE];
    
    // filename counter
    int filecount = 0;
    
    FILE* picture = NULL; 
    
    // check if we've found a jpeg yet or not
    int jpg_found = 0; //false
    
    // go through cardfile until there aren't any blocks left
    while (fread(buffer, BUFFER_SIZE, 1, input) == 1)
    {
        // read first 4 bytes of buffer and see if jpg signature using bitwise on last byte
        if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xe0) == 0xe0)
        {
            if (jpg_found == 1)
            {
                // We found the start of a new pic so close out current picture
                fclose(picture);
            }
            else
            {
                // jpg discovered and now we have the green light to write
                jpg_found = 1;
            }
            
            char filename[8];
            sprintf(filename, "%03d.jpg", filecount);
            picture = fopen(filename, "a");
            filecount++;
        }
        
        if (jpg_found == 1)
        {
            // write 512 bytes to file once we start finding jpgs
            fwrite(&buffer, BUFFER_SIZE, 1, picture);
        }
        
    }

    // close files
    fclose(input);
    fclose(picture);

    return 0;
}

Hello,

The following code is not working, could you please help?
Results :
:) recover.c exists.
:) recover.c compiles.
:) handles lack of forensic image
:( recovers 000.jpg correctly
recovered image does not match
:( recovers middle images correctly
recovered image does not match
:( recovers 049.jpg correctly
recovered image does not match

#include <stdio.h>
#include <stdlib.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>

#define BLOCK 512
#define FILENAME_LENGTH 8

bool isJPEG(unsigned char buffer[]){

if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0)
{
    return true;
}

return false;

}

int main(int argc, char *argv[])
{

//argv[1]
FILE *inFile = fopen(argv[1], "rb");

if (argc != 2)
{
    return 1;
}

if (argv[1] == NULL)
{
    fprintf(stderr, "Usage: ./recover image");
    return 1;
}

//each JPEG file start with a distinct header
//all first 3 bytes in JPEG files are the same : 0xff - 0xd8 - 0xff
// the fourth byte : 0xe0, 0xe1, 0xe2, ...., or 0xef
//the JPEG files are stored back to back in the memory card
//each block is 512 bytes


int count = 0;
unsigned char buffer[BLOCK];
bool found = false;

FILE *outFile;

//read until the end
while (fread(buffer, sizeof(buffer), 1, inFile) == 1)
{

    if (isJPEG(buffer) == true)
    {

        if (found == true)
        {
            // Close outfile
            fclose(outFile);
        }
        else
        {
            found = true;
        }

        char outFileName[FILENAME_LENGTH];

        sprintf(outFileName, "%03i.jpg", count);

        outFile = fopen(outFileName, "wb");

        count++;

        if (found == true)
        {
            if (fwrite(buffer, sizeof(buffer), 1, outFile) != 1)
            {
                fprintf(stderr, "error writing");
            }
        }

    }

}

fclose(outFile);
fclose(inFile);

return 0;

}

Thanks!

hello! could you please explain why the first fread uses buffer while the next fread at the end uses &buffer instead? thank you!

Hi, I had the same doubt. i guess this will help you out, after a bit research i found this answer helpful.
https://stackoverflow.com/a/53471904

why the &buffer ?

it is useless since the buffer array is already a pointer holding the address of the first element in it

Thanks a lot!