I'm trying to solve this problem which consists of reading data from a "memory card" and write it into new readable jpg files.
I'm getting 50 files named correctly as far as I can tell but their data is incorrect. to me it looks like it should be writing into each jpg the data read into the buffer from the card or argv[1] but I'm guessing I'm missing something and I can't figure out what.
this is what I wrote so far:
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
typedef uint8_t BYTE;
int is_jpg(BYTE(buffer[]))
{
if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xe0) == 0xe0)
{
return 1;
}
else
{
return 0;
}
}
int main(int argc, char *argv[])
{
BYTE buffer[512];
//checks argument validity
if (argc != 2)
{
printf("Usage: ./recover image\n");
return 1;
}
FILE *file = fopen(argv[1], "r");
//printf("continuing program\n");
//checks if the file exists
if (file == NULL)
{
printf("No file found\n");
return 2;
}
int file_count = 0;
char file_name[8];
//sprintf(file_name, "%03d.jpg", file_count);
FILE *image;
while (fread(buffer, 512, 1, file) == 1)
{
if (is_jpg(buffer) == 1)
{
if (file_count != 0)
{
fclose(image);
}
sprintf(file_name, "%03d.jpg", file_count);
image = fopen(file_name, "w");
fread(&buffer, 512, 1 , file);
fwrite(&buffer, 512, 1, image);
file_count++;
}
else if (file_count > 0)
{
fwrite(buffer, 512, 1, image);
}
//fwrite(&buffer, 512, 1, image);
}
}
When you detect the header, you do an extra fread [after the image = fopen(file_name, "w"); call].
You want to write the header to the output file/stream. But, the extra fread trashes the header data and the first block of the file is data and not the header as you desire.
You only want the fread at the top of the loop.
Related
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 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;
}
I have been trying to find out what is the issue with my code for hours. I referred to other people's code but I still don't know what's wrong. The code compiles fine but the debugger says that the segmentation fault occurs at line 44 (below the comment). Suggestions to improve my code are welcome too. Please help and thank you.
#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;
}
FILE *f = fopen(argv[1],"r");
if (!f)
{
return 2;
}
BYTE buffer[512];
FILE* img = NULL;
int i = 0;
while (fread(buffer, 512, 1, f) == 1)
{
if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff
&& (buffer[3] & 0xf0) == 0xe0)
{
//create jpeg
char filename[8];
if (img != NULL)
{
fclose(img);
i++;
sprintf(filename, "%03i.jpg",i);
img = fopen(filename, "w");
fwrite(buffer, 512 , 1, img);
}
else
{
sprintf(filename, "%03i.jpg",i);
img = fopen(filename, "w");
//error in the line below :(
fwrite(buffer, 512 , 1, img);
}
}
else if (i > 0)
{
fwrite(buffer, 512 , 1, img);
}
}
fclose(img);
fclose(f);
}
It looks like the most likely failure reason for that line you call out, is that the file handle could be invalid. Hence the first thing I would be doing is checking that every file opens correctly, something like:
img = fopen(filename, "w");
if (img == NULL) {
printf("Error opening file '%s'\n", filename);
exit(1);
}
It's generally a good idea to check for failure conditions in functions than can fail, and this also includes the fwrite calls:
if (fwrite(buffer, 512 , 1, img) != 1) {
printf("Error writing to file\n");
exit(1);
}
I got a segmentation fault with this code. Can anyone help? I have tried a couple of ways but still could not solve the problem. I tried replacing FILE *img = NULL by FILE *img, but it gives another error said variable 'img' is uninitialized when used in fwrite(buffer, 512, 1, img)
#include <stdio.h>
#include <cs50.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
//Open memory card
if (argc != 2)
{
printf("Usage: ./recover image\n");
return 1;
}
FILE *file = fopen(argv[1], "r");
if (!file)
{
return 1;
}
//Read 512 bytes into a buffer
int counter = 0;
unsigned char buffer[512];
char filename[8];
FILE *img = NULL;
while (fread(buffer, 512, 1, file) == 1)
{
if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] && 0xf0 == 0xe0))
{
//If first JPEG
if (counter == 0)
{
//open a new file
sprintf(filename, "%03i.jpg", counter);
img = fopen(filename, "w");
//write the array into the new file
fwrite(buffer, 512, 1, img);
counter++;
}
//if not first JPEG
else
{
//close the file
fclose(img);
//open a new file
sprintf(filename, "%03i.jpg", counter);
img = fopen(filename, "w");
//write the array into the new file
fwrite(buffer, 512, 1, img);
counter++;
}
}
//Else, if already found new JPEG
else
{
fwrite(buffer, 512, 1, img);
}
}
//Close any remaining files
fclose(img);
fclose(file);
return 0;
}
When this if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] && 0xf0 == 0xe0)) is not true (as with the first read), what does program do?
This comment //Else, if already found new JPEG needs to be put into code; ie the following write needs to be conditional.