I'm trying to solve the problem sets of CS50.
Task is, to recover jpegs from data.
My code produces jpegs, but it seems to take just one chunk of 512 bytes instead of the whole picture.
Does my "if" interrupt my "while" condition.
Here my code
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
const int FAT_SIZE = 512;
typedef uint8_t FAT [FAT_SIZE];
typedef uint8_t BYTE;
int main(int argc, char *argv[])
{
if (argc != 2)
{
printf("Usage: ./recover card.raw\n");
return 1;
}
// Open files and determine scaling factor
FILE *input = fopen(argv[1], "r");
if (input == NULL)
{
printf("Could not open file.\n");
return 1;
}
FAT fats;
int number = 0;
char filename[8];
FILE *jpg;
// Going through the input file
while (fread(&fats, 512, 1, input))
{
if (fats[0] == 0xff && fats[1] == 0xd8 && fats[2] == 0xff && (fats[3] & 0xf0) == 0xe0)
{
if (number == 0)
{
sprintf(filename, "%03i.jpg" , 0);
jpg = fopen(filename, "w");
number++;
fwrite(&fats,512, 1, jpg);
} else {
fclose(jpg);
sprintf(filename, "%03i.jpg" , number);
number++;
jpg = fopen(filename, "w");
fwrite(&fats,512, 1, jpg);
}
}
}
fclose(input);
fclose(jpg);
return 0;
}
I found a solution , but I want to understand, why my code is wrong
I didnt write following code. It's written by JosephR , it's just for comparision.
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
typedef uint8_t BYTE;
int main(int argc, char *argv[])
{
if (argc != 2)
{
printf("Usage: ./recover image\n");
return 1;
}
else
{
// Open card.raw
char *input_file_name = argv[1];
FILE *input_pointer = fopen(input_file_name, "r");
if (input_pointer == NULL)
{
printf("Error: cannot open %s\n", input_file_name);
return 2;
}
// Initialise variables
BYTE buffer[512];
int count = 0;
FILE *img_pointer = NULL;
char filename[8];
// Repeat until end of card:
while (fread(&buffer, 512, 1, input_pointer) == 1)
{
// If start of a new JPEG (0xff 0xd8 0xff 0xe*):
if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0)
{
// If not first JPEG, close previous
if (!(count == 0))
{
fclose(img_pointer);
}
// Initialise file
sprintf(filename, "%03i.jpg", count);
img_pointer = fopen(filename, "w");
count++;
}
// If JPEG has been found, write to file
if (!(count == 0))
{
fwrite(&buffer, 512, 1, img_pointer);
}
}
fclose(input_pointer);
fclose(img_pointer);
return 0;
}
}
Related
in this pset I should recover 50 every photo is 512 bytes, I should read the data from a file(argv[1]) then if I found a photo header I should write it to a file but it always gives me uncompleted photos any help would be appreciated
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
int main(int argc, char *argv[])
{
typedef uint8_t BYTE;
if(argc != 2)
{
printf("Usage: ./recover IMAGE\n");
return 1;
}
if (argv[1] == NULL)
{
printf("Usage: ./recover IMAGE\n");
return 1;
}
FILE* out = NULL;
int img_counter= 0;
FILE* memorycard = fopen(argv[1], "r");
if(memorycard == NULL)
{
printf("Could not open %s.", argv[1]);
return 1;
}
BYTE img[512];
char* filename = malloc(9 * sizeof(char));
while (fread (img, 512, 1, memorycard) == 1)
{
if(img[0] == 0xFF && img[1] == 0xD8 && img[2] == 0xFF && (img[3] & 0xF0) == 0xE0)
{
sprintf(filename,"%03i.jpg",img_counter++);
out = fopen(filename,"a");
fwrite(img,512,1,out);
fclose(out);
}
}
fclose(memorycard);
return 0;
}
So I'm trying CS50 Recover exercise (where you need to search for jpg files in a memory card and whenever you find one- you open a new file and write the jpg found to the new file). My code compiles and returns 51 jpegs instead of only 50 and all of them are incorrect. Please, I need some cues on what to focus at and fix/replace.
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
typedef uint8_t BYTE;
int main(int argc, char *argv[])
{
// Check for valid usage
if ( argc != 2)
{
printf("Usage: ./recover IMAGE\n");
return 1;
}
// Check for valid image
FILE *image = fopen(argv[1], "r");
if (image == NULL)
{
return 1;
}
BYTE buffer[512];
int i = 0;
char new_image[8];
FILE *output;
FILE *output1;
while (fread (buffer, 1, 512, image) == 512)
{
// IF Start of a JPEG
if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && ((buffer[3] & 0xf0) == 0xe0))
{
sprintf(new_image, "%03i.jpg", i);
//if first JPEG
if ( i == 0)
{
output = fopen(new_image, "w");
fwrite(buffer, 512, 1, output);
i++;
}
// if not first JPEG
else
{
fclose(output);
sprintf(new_image, "%03i.jpg", i);
output1 = fopen(new_image, "w");
fwrite(buffer, 1, 512, output1);
fclose(output1);
i++;
}
}
// if not start of a JPEG
else
{
output = output1 = fopen(new_image, "w");
fwrite(buffer, 1, 512, output);
}
}
fclose(image);
}
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
int blocksize = 512;
int main(int argc, char *argv[])
{
if( argc != 2 )
{
printf("mention the file name or too many commands\n");
return 1;
}
FILE *in = fopen(argv[1], "r");
FILE *out;
if (in == NULL)
{
printf("could not open the file %s", argv[1]);
return 1;
}
uint8_t buffer[blocksize];
int count = 0;
int precount = 1;
int flag = 1;
while(fread(buffer, sizeof(uint8_t), 512, in) == blocksize)
{
if((buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && ((buffer[3] & 0xf0) == 0xe0)) || flag == 1)
{
if (flag == 0)
{
char filename[9];
sprintf(filename, "%03i.jpg", count);
out = fopen(filename, "w");
count++;
flag = 1;
}
if(count == precount)
{
fwrite(buffer, sizeof(uint8_t), 512, out);
}
else
{
fclose(out);
precount++;
flag = 0;
}
}
}
return 0;
}
First I am searching for headers then once I find it, I write it in the out file.
I want to keep writing until I find the required headers again and then I want to close the existing file and open a new file until I find those headers again.
Now the problem is when I declare the FILE *out inside the if statement it becomes if's local variable and if I do this the way the code here I get seg fault.
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
int main(int argc, char *argv[])
{
// open memory card
if(argc > 2 )
{
printf("Usage: ./recover image");
return 1;
}
FILE *file = fopen(argv[1], "r");
FILE *img;
// repeat until end
int i = 0;
// 512 bytes into buffer
uint8_t buffer[2048];
char *filename = malloc(8);
// if start of new jpeg
while(fread(&buffer, 512, 4, file)) // read card
{
if(buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0) // if start new jpeg
{
// if first
i++;
sprintf(filename, "%03i.jpg", i);
img = fopen(filename, "w");
fwrite(&buffer, sizeof(uint8_t), 1, img); // fixed
}
//else
else
{
// if still reading jpeg
if(img != NULL)
{
fwrite(&buffer, sizeof(uint8_t), 1, img);
}
}
}
//close
free(filename);
fclose(file);
return 0;
}
I think my code is pretty close to being done but the images returned are invalid or unsupported image format. It compiles fine and it returns 12 images. I do not want to look at a solution to fix this. Where did my code mess up?
I'm always getting a segfault when trying to run the code.
I think it is caused by the last lines fclose(file) and fclose(img), but I don't really seem to understand why exactly.
If I delete both lines nothing happens.
Could someone please explain to me why segfault is called and why it is not creating new .jpg's?
(I have to implement a program that recovers JPEGs from a forensic image)
https://cs50.harvard.edu/college/2020/fall/psets/4/recover/
#include <stdlib.h>
#include <stdint.h>
#include <cs50.h>
int main(int argc, char *argv[])
{
//open file
FILE *file = fopen(argv[1], "r");
//promting user
if(argc != 2)
{
printf("Usage: ./recover image\n");
return 1;
}
else if (file == NULL)
{
printf("Empty file.\n");
return 2;
}
int i = 0;
int found = 0;
unsigned char buffer[512];
FILE *img = NULL;
while (fread(buffer, 512, 1, file))
{
//start of new Jpeg?
if (buffer[0] == 0xff && buffer[1] == 0xff && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0)
{
//close file if found
if(found == 1)
{
fclose(img);
}
// open new one
else
{
found = 1;
}
char filename[8];
sprintf(filename, "%03i.jpg", i);
img = fopen(filename, "w");
i++;
}
if(found == 1)
{
fwrite(buffer, 512, 1, img);
}
}
fclose(file);
fclose(img);
return 0;
}