Answered - CS50 PSet4 Recover: Getting Segmention fault (core dumped) - cs50

Question

I am getting a 'Segmentation fault (core dumped) error'
I know that means I am accessing memory I shouldn't.
The error is coming in the outer else loop with the fwrite function. fwrite(buffer, 1, 512, img);
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
int main(int argc, char *argv[])
{
if (argc != 2)
{
printf("Usage: ./recover IMAGE\n");
return 1;
}
FILE *file = fopen(argv[1], "r");
if (file == NULL)
{
printf("File entered does not exist\n");
return 1;
}
typedef uint8_t BYTE;
BYTE buffer[512];
char filename[8];
int i = 0;
FILE *img;
while (fread(buffer, 1, 512, file) == 512)
{
// check if first three bytes are 0xff 0xd8 0xff
// check if 4th byte is 0xe0, 0xe1, 0xe2, ..., 0xef
// if those 4 bytes are found then start writing these bytes to a file ###.jpg
// once you see the 4 bytes again, stop writing to the current file and make a new file ###.jpg to write to
if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0)
{
if (i == 0)
{
sprintf(filename, "%03i.jpg", i);
img = fopen(filename, "w");
i += 1;
}
else
{
fclose(img);
sprintf(filename, "%03i.jpg", i);
img = fopen(filename, "w");
i += 1;
}
fwrite(buffer, 1, 512, img);
}
else
{
fwrite(buffer, 1, 512, img);
}
}
fclose(img);
return 0;
}
Any ideas, hints or tips would be appreciated.
This is my first time posting in stackoverflow :D
Solved:
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
int main(int argc, char *argv[])
{
if (argc != 2)
{
printf("Usage: ./recover IMAGE\n");
return 1;
}
FILE *file = fopen(argv[1], "r");
if (file == NULL)
{
printf("File entered does not exist\n");
return 1;
}
typedef uint8_t BYTE;
BYTE buffer[512];
char filename[8];
int i = 0;
FILE *img;
while (fread(buffer, 1, 512, file) == 512)
{
// check if first three bytes are 0xff 0xd8 0xff
// check if 4th byte is 0xe0, 0xe1, 0xe2, ..., 0xef
// if those 4 bytes are found then start writing these bytes to a file ###.jpg
// once you see the 4 bytes again, stop writing to the current file and make a new file ###.jpg to write to
if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0)
{
if (i == 0)
{
sprintf(filename, "%03i.jpg", i);
img = fopen(filename, "w");
i += 1;
}
else
{
fclose(img);
sprintf(filename, "%03i.jpg", i);
img = fopen(filename, "w");
i += 1;
}
fwrite(buffer, 1, 512, img);
}
else
{
if (i > 0)
{
fwrite(buffer, 512, 1, img);
}
}
}
fclose(img);
return 0;
}