CS50 recover doesn't output any images - c

Question

I'm working on the recover program of the CS50 course. Here are the instructions:
Implement your program in a file called recover.c in a directory called recover.
Your program should accept exactly one command-line argument, the name of a forensic image from which to recover JPEGs.
If your program is not executed with exactly one command-line argument, it should remind the user of correct usage, and main should
return 1.
If the forensic image cannot be opened for reading, your program should inform the user as much, and main should return 1.
Your program, if it uses malloc, must not leak any memory.
I think my code is supposed to work, but it doesn't. In fact, it doesn't output any images at all! Here's the code:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
FILE * pFile = NULL;
unsigned char *buffer = malloc(512);
char* filename = NULL;
int filenumber = 0;
//If user didn't print 2 items
if(argc != 2)
{
printf("Usage: ./recover image\n");
return 1;
}
//Open the file
pFile = fopen(argv[1], "r");
if (!pFile)
{
fprintf(stderr, "File cannot be opened\n");
return 2;
}
int j=0;
// checking the card by 512b chunks
//loop (i=0, i++);
while (pFile)
{
int i =0;
i++;
//k=fread (buffer, 512, i, *file);
int k = fread(buffer, 512, i, pFile);
// if 512 byte block is jpeg, make new jpeg file
if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0)
{
// if it's not the first file, we should close the last one
if (filename != NULL)
{
fclose(pFile);
}
//sprintf
sprintf(filename, "%03i.jpg", 2);
//FILE = fopen (W)
pFile = fopen(filename, "w");
// fwrite (buffer, 512, j, *file1)
fwrite (buffer, 512, j, pFile);
//j=j+1
j = j + 1;
}
// if k<512 - end of the loop
if (k < 512)
{
return 0;
}
}
free(buffer);
}
I don't understand it, but I see no new files or JPEGs pop-up in my files. When I try to double-click on the file, which is called card.raw, it doesn't let me open it.

Answer 1

You have a load of problems. Running your code in a debugger should reveal most of them within a second.
Let's take a look:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
FILE * pFile = NULL;
unsigned char *buffer = malloc(512);
char* filename = NULL; <<==== You never allocate any memory for this. Use an array.
int filenumber = 0;
//If user didn't print 2 items
if(argc != 2)
{
printf("Usage: ./recover image\n");
return 1;
}
//Open the file
pFile = fopen(argv[1], "r");
if (!pFile)
{
fprintf(stderr, "File cannot be opened\n");
return 2;
}
int j=0;
// checking the card by 512b chunks
//loop (i=0, i++); <<== No information provided by this comment.
while (pFile) <<== pFile is your input file. This should never change. ???
{
int i =0;
i++;
//k=fread (buffer, 512, i, *file); <<== Useless comment. Nearly same as code below but causes compiler error
int k = fread(buffer, 512, i, pFile); <<== i is always 1 and must be 1. Don't use variable.
<<== BTW: You should check k **before** using the buffer.
// if 512 byte block is jpeg, make new jpeg file
if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0)
{
// if it's not the first file, we should close the last one
if (filename != NULL)
{
fclose(pFile); <<== Yikes!!! This is your input file.
}
//sprintf <<== Yes, that's obvious. Useless comment.
sprintf(filename, "%03i.jpg", 2); <<== Yikes!! You never allocate memory. NULL pointer!!
<<== Why do you always print 2? you have a counter.
//FILE = fopen (W) <<== Again no useful information in comment
pFile = fopen(filename, "w"); <<== Feed NULL into fopen and kill pFile.
// fwrite (buffer, 512, j, *file1) <<== you know what I mean...
fwrite (buffer, 512, j, pFile); <<== You only have 1 buffer, why write j blocks?
//j=j+1 <<== obvious
j = j + 1;
}
// if k<512 - end of the loop
if (k < 512) <<== fread returns number of elements, i.e. 1, not number of bytes.
{
<< you return without
- closing files
- freeing buffer
return 0;
}
<<== Now you go back to top of the loop and want to read next block from your raw file but pFile was killed in the loop.
}
free(buffer);
}