Re: C standard question?

jan.chludzinski@[EMAIL PROTECTED]
 wrote:
> 
> Are the variables on the righthand side of an assignment statement
> treated strictly as values?  That is, if in assigning to an
> "unsigned int" I ****ft a "unsigned char" 24 places to the left,
> can I trust that the compiler will use temp storage sufficient to
> hold the "unsigned int" and NOT result in an overflow (because I
> ****fted an "unsigned char" 24 places)?
> 
> Using gcc I tried the code below:
> 
> #include <stdio.h>
> int main( int argc, char *argv[] ) {
>     unsigned char c[ 4 ] = { 0xff, 0xff, 0xff, 0xff };
>     unsigned int ui;
> 
>     ui = (c[ 3 ] << 24) | (c[ 2 ] << 16) | (c[ 1 ] << 8) | c[ 0 ];
>     fprintf( stderr, "ui = %x\n", ui );
> }
> 
> and got:    ui = ffffffff

That only worked because the default int in your system was a 32
bit quantity.  You need to ensure that the various c[n]s are
converted to a 32 bit quantity before ****fting, i.e. cast them to
unsigned long (not int), as in: "((unsigned int)c[3] << 24) |
((unsigned int)c[3] << 16) ...".

-- 
 [mail]: Chuck F (cbfalconer at maineline dot net) 
 [page]: <http://cbfalconer.home.att.net>
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