Re: Warning when initializing a long variable

[Bob Soliday <soliday@aps.anl.gov>]

Bob Soliday wrote:
> Schoeneburg, Bernd wrote:
> > Hi all,
> > when I try to initalize a long variable with the most negative value 
> > of -2147483648 which should be 0xFFFFFFFF, then I get a compiler 
> > warning. The compiler is gcc version 3.4.5 running on solaris.
> >
> > long test_var = -2147483648L;
> > ....
> > ../devPbdp.c:80: warning: decimal constant is so large that it is 
> > unsigned
> >
> > -2147483647 is accepted. This problem exists only with long. char and 
> > short can be initialized to the most negative values without any problem.
> >
> > Any idea? Thank you....
> >
> > - Bernd
> /usr/include/sys/types.h defines LONG_MIN as -2147483647L-1L
>
> I don't know why they defined it this way but I assume there
> is a reason.
>
> --Bob
>

I have figured out the reason this works. The language syntax definition 
doesn't define negative number literals, rather the negative numbers are 
generated by the unary - operator. What this means is that it is not 
reading -2147483648L the way you think it is. Instead it is reading it 
as -(2147483648L). Since 2147483647L is equal to LONG_MAX it does not 
know what to do with a number even bigger.