我的代码出现分段错误

Question

I am writing a code that reads information from a memory card (card.raw is the one we are provided but the code uses user input) and extracts the jpegs from it using the signatures that jpegs have of (0xff,0xd8,0xff,0x00 - 0xff). I am getting a segmentation fault because i am using malloc, but i dont see where i went wrong. I am pasting my code here any help would be appreciated.

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


typedef uint8_t BYTE;

int main(int argc, char *argv[])
{
    //check terminal usage
    if (argc != 2)
    {
        printf("Usage: ./recover image");
        return 1;
    }

    //open inputted file and check for valid file
    FILE *file = fopen(argv[1], "r");
    if (!file)
    {
        printf("Invalid or missing file.");
        return 1;
    }

    BYTE *buff = malloc(512 * sizeof(BYTE));
    int counter = 0;
    FILE *image = NULL;
    char *name = malloc(8 * sizeof(char));

    //loop till end of file reached and read a block of input
    while(fread(buff, sizeof(BYTE), 512, file) == 1 && !feof(file))
    {
        bool foundJPEG = buff[0] == 0xff && buff[1] == 0xd8 && buff[2] == 0xff && ((buff[3] & 0xf0) == 0xe0);

        //check if found jpeg, and open file for writing
        if (foundJPEG)
        {
            sprintf(name, "%03i.jpg", counter);
            image = fopen(name, "w");
        }
        //if image file open, write to it
        if (image != NULL)
        {
            fwrite(buff, sizeof(BYTE), 512, image);
        }
        //if found a jpeg already, close it so new one can be written
        if (foundJPEG && image != NULL)
        {
            fclose(image);
            counter++;
        }

    }

    free(name);
    free(buff);
    fclose(image);
    fclose(file);
    return 0;

}

Answer 1

There are three issues with the code above which are not mentioned in the comments:

The return value of fread is not 1 but 512, upon successful read. You exchanged the parameters for the blocksize and the blockcount -> fread definition . Therefore the while loop is not entered. Don't try to save space with packing to much code into one statement. If would be more clever to separate the checks for the fread return value and the EOF and use a do... while() loop, instead. Then you had the chance of seeing this issue in the debugger. This was exactly what i have done and how i found this out.

The second issue is that you close the image after rescuing the first 512 bytes, but you do not reset the file pointer image back to NULL along with the fclose statement. As a consequence, the code would repeatedly write to an a file which is closed until a new block with a jpg header is found.

The third issue is that you only rescue the first 512 bytes of the jpg but not the whole jpg. You need to scan the input stream for the jpg end indicator FF D9 and copy bytes until it is found. -> jpg format