#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
/**
Processes a pixel by forming the negative.
@param blue the blue value of the pixel
@param green the green value of the pixel
@param red the red value of the pixel
*/
void process(int& blue, int& green, int& red)
{
   blue = 255 - blue;
   green = 255 - green;
   red = 255 - red;
}
/**
Gets an integer from a binary stream.
@param stream the stream
@param offset the offset at which to read the integer
@return the integer starting at the given offset
*/
int get_int(fstream& stream, int offset)
{
   stream.seekg(offset);
   int result = 0;
   int base = 1;
   for (int i = 0; i < 4; i++)
   {
      result = result + stream.get() * base;
      base = base * 256;
   }
   return result;
}
int main()
{
   cout << "Please enter the file name: ";
   string filename;
   cin >> filename;
   fstream stream;

   // Open as a binary file
   stream.open(filename.c_str(),
      ios::in|ios::out|ios::binary);

   // Get the image dimensions
   int file_size = get_int(stream, 2);
   int start = get_int(stream, 10);
   int width = get_int(stream, 18);
   int height = get_int(stream, 22);
   // Scan lines must occupy multiples of four bytes
   int scanline_size = width * 3;
   int padding = 0;
   if (scanline_size % 4 != 0)
   {
      padding = 4 - scanline_size % 4;
   }
   if (file_size != start +
      (scanline_size + padding) * height)
   {
      cout << "Not a 24-bit true color image file.“
         << endl;
      return 1;
   }
   // Go to the start of the pixels
   stream.seekg(start);

   // For each scan line
   for (int i = 0; i < height; i++)
   {
      // For each pixel
      for (int j = 0; j < width; j++)
      {
         // Go to the start of the pixel
         int pos = stream.tellg();

         // Read the pixel
         int blue = stream.get();
         int green = stream.get();
         int red = stream.get();
         // Process the pixel
         process(blue, green, red);

         // Go back to the start of the pixel
         stream.seekp(pos);
         stream.put(blue);

         // Write the pixel
         stream.put(green);
         stream.put(red);
      }

      // Skip the padding
      stream.seekg(padding, ios::cur);
   }
   return 0;
}