Mail Archives: djgpp/1998/05/08/16:01:38
hi !
The problame is:
GCC alignes data. GCC produces long aligned data.
If you have a short, it will allocate 4 bytes.
And it will use only the first two bytes of the 4 byte allocated in the
structure.
But if you have two shorts, it will put them in ONE long.
So totalmemory and oem_software_rev will be in ONE long.
but vbe version will use 4 bytes.
unsigned char reserved[222] will lose two bytes space.
Pentium CPU can run faster if you use long aligned data.
I would recommend to lose some memory and use long aligned data.
WT wrote:
> I am trying to write a short program to detect VESA VBE and output
> information about the video card. I declared a struct of 512 bytes to be
> used as a buffer for vbe_info_block. The strange thing is that when I
> printed sizeof(vbe_info_block) it gave me 516 bytes instead of 512. I am
> sure my struct is correct because I've checked it many times. This is
> how the struct is declared :
>
> typedef
> struct {
> unsigned int vbe_signature; /* VBE Signature */
4
> unsigned short vbe_version; /* VBE Version */
8
> unsigned int oem_string_ptr; /* Pointer to OEM info */
12
> unsigned int capabilities; /* Capabilities of graphics controller */
16
>
>
> unsigned int video_mode_ptr; /* Pointer to VideoModeList */
20
> unsigned short total_memory; /* Number of 64kb memory blocks */
22
> /* Added for VBE 2.0 */
> unsigned short oem_software_rev; /* VBE implementation Software
24
> revision */
> unsigned int oem_vendor_name_ptr; /* Pointer to Vendor Name String
28
> */
> unsigned int oem_product_name_ptr; /* Pointer to Product Name String
32
> */
> unsigned int oem_product_rev_ptr; /* Pointer to Product Revision
36
> String */
> unsigned char reserved[222]; /* Reserved for VBE implementation
260
> scratch area */
> unsigned char oem_data[256]; /* Data Area for OEM Strings */
516
I won ! :-))
> } vbe_info_block;
>
> Could it be something wrong with the int declaration? Please help!
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