sizeof( ) doesn't add up!

[ChuckB]

Hi,

I noticed something quirky with getting the size of a structure and comparing that to the sum of its individual parts. The size of the structure is 16 but the sum of the parts total 14. Any explanations? :-)
Regards,
ChuckB

  typedef struct {
    unsigned short type;       //WORD
    unsigned long size;        //DWORD
    unsigned short reserved1;  //WORD
    unsigned short reserved2;  //WORD
    unsigned long offset;      //DWORD
  } HEADER;  
  HEADER h;

  cout <<"type: " << sizeof(h.type) << endl;                    //2 bytes
  cout <<"size: " << sizeof(h.size) << endl;                      //4 bytes
  cout <<"reserved1: " << sizeof(h.reserved1) << endl;  //2 bytes
  cout <<"reserved2: " << sizeof(h.reserved2) << endl;  //2 bytes
  cout <<"offset: " << sizeof(h.offset) << endl;                //4 bytes
  cout <<"---------------------" << endl;
  cout <<"Size of h: " << sizeof(h) << endl << endl;;       //16 bytes
  cout <<"Size of HEADER: " << sizeof(HEADER) << endl; //16 bytes

[transcendental]

It seems that parksie was correct here.

http://www.vbforums.com/showthread.p...TMAPFILEHEADER

Look at the 4th post from the last.

http://www.codeguru.com/forum/showth...ighlight=ALIGN

Use #pragma pack to make your own structure 16 bytes, just like Windows' equivalent.

Hope it helps.

[ChuckB]

Hi,
Thanks for the tip on 'pragma pack'. If you noticed your first link, I started that thread, but got lost listening to the 'pros' talk. I'll experiment with this boundary stuff.

Thanks,
ChuckB

[transcendental]

Maybe you would like to look up the declaration of tagBITMAPFILEHEADER in wingdi.h, and pshpack2.h and poppack.h . Something is there!