Re: [Mingw-users] RE: bit operatons

[Greg C. <chi...@mi...>]

"Henning, Brian" wrote:
> 
> I am trying to store 4 unsigned char's in an unsigned long with the following code.
> Is there a better way of doing this other than the way i have presented?
> 
> long result;
>     if( fread(bytes, sizeof(unsigned char), 4, ifp) != 4 ) {

BTW, the language defines sizeof(unsigned char) to be 1.
Using sizeof here doesn't make the code more portable.
Maybe you want CHAR_BIT instead of 8 below, though.
But if you want the data files to be portable, then
byte order will get in the way.

>         fprintf(stderr, "Cannot read the bytes of this file\n");
>         exit(1);
>     }
>     result = (result << 8) | bytes[3];
>     result = (result << 8) | bytes[2];
>     result = (result << 8) | bytes[1];
>     result = (result << 8) | bytes[0];
>     height = result;

Wouldn't this
  fread(&result, sizeof(long), 1, ifp)
do the same thing more simply?