bitmap file ..

[mad_muppet]

I am trying to write a bitmap file taking BMP file format - Wikipedia, the free encyclopedia as my reference .. I am trying to write the 2x2 bitmap.

the code compiles and runs ok but when I try and open the file I get an error "cannot be displayed, because it contains errors"

any help appreciated thanks in advance al.

//objective write bimap from
// http://en.wikipedia.org/wiki/BMP_file_format#Bitmap_file_header
#include<stdio.h>
#include<stdlib.h>
#include<inttypes.h>

struct bmpfile{
  unsigned char    magic[2];
}bf,*p;
struct fileheader{
  uint32_t         filesize;
  uint16_t         creator1;
  uint16_t         creator2;
  uint32_t         bmpoffset;
}fh,*fhp;
struct bmpinfoheader{
  uint32_t        headersize;
  int32_t         width;
  int32_t         height;
  uint16_t        nplanes;
  uint16_t        bitsperpixel;
  uint32_t        compressiontype;
  uint32_t        bitmapbytesize;
  int32_t         hres;
  int32_t         vres;
  uint32_t        ncolors;
  uint32_t        nimpcolors;
}bh,*bhp;

int main(){
  printf("main\n");
 
  int c;
  FILE *fp;
  unsigned char array[16],*pp;
  pp = array;
  p = &bf;
  fhp = &fh;
  bhp = &bh;

 printf("set array to zero\n");
  for( c = 0; c <= 16; c++ ){
    pp[c] = 0;
  }
  printf("colors\n");

  pp[0] = 255;
  pp[3] = 255;
  pp[4] = 255;
  pp[5] = 255;
  pp[8] = 255;
  pp[12] = 255;
 
  p->magic[0] = 'B';
  p->magic[1] = 'M';
  printf("set bm\n");
 
  fhp->filesize = 70;
  fhp->bmpoffset = 54;
  fhp->creator1 = 0;
  fhp->creator2 = 0;
  printf("set filesize\n");

  bhp->width = 2;
  bhp->height = 2;
  bhp->nplanes = 1;
  bhp->bitsperpixel = 24;
  bhp->compressiontype = 0;
  bhp->bitmapbytesize = 16;
  bhp->hres = 2835;
  bhp->vres = 2835;
  bhp->ncolors = 0;
  bhp->nimpcolors = 0;
  bhp->headersize = bhp->bitsperpixel + bhp->bitmapbytesize;
  printf("bitmapinfoheader\n");

  fp = fopen("foo.bmp","ab");
  printf("fopen\n");

  fwrite(p,sizeof(bf),1,fp);
  printf("bfp\n");

  fwrite(fhp,sizeof(fh),1,fp);
  printf("fhp\n");

  fwrite(bhp,sizeof(bh),1,fp);
  printf("bhp\n");
 
  fwrite(array,sizeof(array),1,fp );
  // fwrite( p,sizeof(array[ 0 ]),16,fp );
  printf("array\n");
 
  fclose( fp );
  printf("close\n");

  return( 0 );
}

[anduril462]

Read this: Data structure alignment - Wikipedia, the free encyclopedia.

I don't know what compiler you're using and whether #pragma pack will work for you (you want single-byte alignment). You can always write out the struct components one-by-one to be safe.

[dylan]

Your fopen is appending to the file.
If you have a bad file you're just adding data to it.

Dylan