PSET4 Recover Segmentation Fault Help

Question

Edit: It has been resolved. I figured it out. Anyone who has similar problem may check my answers below. Try to skip over my code to avoid spoiling yourself.

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I have been stuck with Recover since last week. My program outputs a segmentation fault whenever I run it. Can anyone please help take a look and make some suggestions? Thanks in advance. Here is my code:

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

//main function
int main(int argc, char *argv[])
{
    //declaring input and output file pointers
    FILE * inptf, *otptf = NULL;

    //checks if user entered prompt
    if (argc != 2)
    {
        printf("Usage: ./recover image\n");
        return 1;
    }

    //open input file to be read
    inptf = fopen(argv[1], "r");

    //check if file is readable
    if (inptf == NULL)
    {
        printf("File not Found.\n");
        return 2;
    }

    //count images found
    int img_count = 0;

    //store image name
    char img_name[8];

     //allocates memory for 1 block of data
    unsigned char * block = malloc(512);


    //loop to read the entire card until the end of file
    while (fread(&block, 1, 512, inptf) == 512)
    {
        //checks for image header
        if (block[0] == 0xff && block[1] == 0xd8
                             && block[2] == 0xff
                             && (block[3] & 0xf0) == 0xe0)
            {
                //if a non-first image is found
                if (img_count > 0)
                {
                    fclose(otptf);
                }

                //create file name
                sprintf(img_name, "%03i.jpg", img_count);

                //open output file to write
                otptf = fopen(img_name, "w");

                //write image into file
                fwrite(&block, 1, 512, otptf);

                //increment number of image found
                img_count++;
            }

            else
            {
                //if an image has been found
                if (img_count > 0)
                {
                    //continue writing image into memory
                    fwrite(&block, 1, 512, otptf);
                }
            }

            //free block of memory
            free(&block);

            //goes to new block
            fseek(inptf, 1, SEEK_CUR);
        }

    //close output image file
    fclose(otptf);

    //close memory card
    fclose(inptf);

    return 0;
}

Here are the results from check50:

:) recover.c exists.
:) recover.c compiles.
:) handles lack of forensic image
:( recovers 000.jpg correctly
    failed to execute program due to segmentation fault
:( recovers middle images correctly
    failed to execute program due to segmentation fault
:( recovers 049.jpg correctly
    failed to execute program due to segmentation fault

Answer 1

Nevermind, I figured it out by solving 2 problems:

1. I converted the buffer into an array instead of using malloc. It works wonderfully, and I wished I had realized it sooner.

2. I deleted one line of code at the end of the while loop (fseek). I thought it was significant, but randomly deleting lines of codes when you are desperate solves the problem.