gistfile1.c

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

#define BUFFER_SIZE 512

void IncStr(char*);
bool AllZeros(uint8_t*, size_t);

int main(int argc, char* argv[])
{
    // Open the file storing the JPEGs
    FILE* fp = fopen("card.raw", "r");
    
    if (fp == NULL)
    {
        return 1;
    }
    
    // n_str is the name of the extracted JPEGs, it starts at 000 and increments
    char n_str[4];
    n_str[0] = n_str[1] = n_str[2] = '0';
    n_str[3] = '\0';
    
    // ending is ".jpg"
    char ending[5];
    ending[0] = '.';
    ending[1] = 'j';
    ending[2] = 'p';
    ending[3] = 'g';
    ending[4] = '\0';
    
    // Open the first extracted JPEG's destination
    FILE* current_fp = fopen(strcat(n_str, ending), "w");
    
    if (current_fp == NULL)
    {
        return 2;
    }
    
    uint8_t read_count = 0;
    while (1)
    {
        // Creates a buffer
        uint8_t buffer[BUFFER_SIZE];
        
        // Reads a memory block into the buffer from the file
        int r = fread(buffer, sizeof(uint8_t), BUFFER_SIZE, fp);
	if (r != BUFFER_SIZE * size(uint8_t)
	{
		return 3;
	}
        read_count++;
        
        // If the buffer begins a new JPEG
        if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] == 0xe0 || buffer[3] == 0xe1) && read_count > 1)
        {
            // Closes the current file
            fclose(current_fp);
            
            // Increments the file name
            IncStr(n_str);
            
            // Opens the new file
            current_fp = fopen(strcat(n_str, ending), "w");
            
            if (current_fp == NULL)
            {
                return 4;
            }
            
            // Writes the buffer to the new file
            fwrite(buffer, sizeof(uint8_t), BUFFER_SIZE, current_fp);
        } else if (AllZeros(buffer, BUFFER_SIZE))
        {
            fclose(current_fp);
        
            break;
        } else
        {
            fwrite(buffer, sizeof(uint8_t), BUFFER_SIZE, current_fp);
        }
    }
    
    fclose(fp);
    
    return 0;
}

void IncStr(char* s)
{
    if (sizeof(s) * sizeof(char) != 4)
    {
        return;
    }
    
    int n = atoi(s);
    
    n++;
    
    if (n < 10)
    {
        sprintf(s + 2, "%d", n);
        s[0] = s[1] = '0';
    } else if (n < 100)
    {
        sprintf(s + 1, "%d", n);
        s[0] = '0';
    } else if (n < 1000)
    {
        sprintf(s, "%d", n);
    }
}

bool AllZeros(uint8_t* block, size_t size)
{
    for (int i = 0; i < size; i++)
    {
        if (block[i] != 0)
        {
            return 0;
        }
    }
    
    return 1;
}