Read windows bitmap graphic

[Cooker]

Hi,
I want to read a graphic(Width:266,Height:341).
After reading this graphic, I will do something on it and store it.
I write the following codes:

#include <stdio.h>
#include <windows.h>

int main()
{
   BITMAPFILEHEADER bmheader;
   BITMAPINFOHEADER bm;

   FILE *fp;
   unsigned char *data;

   fp = fopen("origin.bmp","rb");
   if ( fp == NULL ) {
      printf("Cannot open file!\n");
      return -1;
   }

   fread(&bmheader,1,sizeof(BITMAPFILEHEADER),fp);
   fread(&bm,1,sizeof(BITMAPINFOHEADER),fp);
   data = (unsigned char *)malloc(bm.biHeight*bm.biWidth*3*sizeof(unsigned char)); 
   fread(data,1,bm.biHeight * bm.biWidth * 3,fp);
   fclose(fp);

   // do something...

   fp = fopen("result.bmp","wb");
   fwrite(&bmheader,1,sizeof(BITMAPFILEHEADER),fp);
   fwrite(&bm,1,sizeof(BITMAPINFOHEADER),fp);
   fwrite(data,1,bm.biHeight * bm.biWidth * 3, fp);

   fclose(fp);
   free(data);
   return 0;
}

I just write the read and store parts.
But I find that the stored graphic can't display correctly.
I think the size of graphic file is 272172 bytes.
( sizeof(BITMAPFILEHEADE) + sizeof(BITMAPINFOHEADER) + raster data( 3 * Width * Height) )
But I find the size of graphic file is 272854. The difference is 682 ( 272854-272172).
What' s the purpose of the 682 bytes?
And what shall I do to store correctly?
Thank you!

[Marc G]

The size of each scanline of a windows bitmap should be a multiple of a DWORD.

[Cooker]

The size of each scanline of a windows bitmap should be a multiple of a DWORD.

Thank you!
I already solve it!