Unary minus applied to unsigned int

[Andrew Ward]

Hi All,
I tried to compile the following line:
pair<long, ulong> cr3(make_pair(-2147483648L, 2147483647));

but get this error:
unary minus applied to unsigned type, result still unsigned.

But in my c++ book is says that the postfix L forces the integer to be
signed.

Could anyone please explain this behaviour, and if possible point me to some
documentation that explains how intergral types are handled in depth?

Andy

[Tõnu Aas]

Re: Unary minus applied to unsigned int

> I tried to compile the following line:[color=blue]
> pair<long, ulong> cr3(make_pair(-2147483648L, 2147483647));[/color]

2147483648L > MAX LONG, so compiler silently uses unsigned long instead.
Its some compiler bug, because -2147483648L is nice signed long constant.

Tõnu.

[Ron Natalie]

Re: Unary minus applied to unsigned int


"Andrew Ward" <anwar@ihug.co. nz> wrote in message news:r1ucb.1583 30$JA5.3889031@ news.xtra.co.nz ...
[color=blue]
> But in my c++ book is says that the postfix L forces the integer to be
> signed.[/color]
The number is too big for (signed) long so it becomes unsigned long.
There are no negative literals, just positive ones with a unary minus
applied to it. There is no way to represent that number with a literal
I expect on your environment.

However, you can use numeric_limits< long>::min() to get the value.
Probably a better idea than hardcoding those number in anyhow.

[Jerry Coffin]

Re: Unary minus applied to unsigned int

In article <3f72b7c0$1@new s.infonet.ee>, tonu@ids.ee says...

[ ... ]
[color=blue]
> 2147483648L > MAX LONG, so compiler silently uses unsigned long instead.
> Its some compiler bug, because -2147483648L is nice signed long constant.[/color]

Unfortunately this isn't correct. The problem is that this is NOT
parsed as simply a negative constant. It's parsed as a unary minus
operator, followed by a positive constant. Unfortunately, on a typical
32-bit system, 2147483648L is too large to be a signed long constant, so
it's treated as an unsigned long constant. The unary minus is then
applied to that unsigned long, and about the only (sort of) good result
is a warning message telling you that you haven't gotten what you
probably wanted.

--
Later,
Jerry.

The universe is a figment of its own imagination.

[Mike Wahler]

Re: Unary minus applied to unsigned int


"Tõnu Aas" <tonu@ids.ee> wrote in message news:3f72b7c0$1 @news.infonet.e e...[color=blue][color=green]
> > I tried to compile the following line:
> > pair<long, ulong> cr3(make_pair(-2147483648L, 2147483647));[/color]
>
> 2147483648L > MAX LONG, so compiler silently uses unsigned long instead.
> Its some compiler bug, because -2147483648L is nice signed long constant.[/color]

That value is not required to be in the range of
signed long. A value one greater is, however.

-Mike

[Jack Klein]

Re: Unary minus applied to unsigned int

On Thu, 25 Sep 2003 16:19:33 +1200, "Andrew Ward" <anwar@ihug.co. nz>
wrote in comp.lang.c++:
[color=blue]
> Hi All,
> I tried to compile the following line:
> pair<long, ulong> cr3(make_pair(-2147483648L, 2147483647));[/color]

Replace -2147483648L with (-2147483647 - 1)
[color=blue]
>
> but get this error:
> unary minus applied to unsigned type, result still unsigned.
>
> But in my c++ book is says that the postfix L forces the integer to be
> signed.
>
> Could anyone please explain this behaviour, and if possible point me to some
> documentation that explains how intergral types are handled in depth?
>
> Andy[/color]

--
Jack Klein
Home: http://JK-Technology.Com
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[Ron Natalie]

Re: Unary minus applied to unsigned int


"Jack Klein" <jackklein@spam cop.net> wrote in message news:dmd7nv8ocd verf4a62d8n06tb 6lnn1q7hf@4ax.c om...[color=blue]
> On Thu, 25 Sep 2003 16:19:33 +1200, "Andrew Ward" <anwar@ihug.co. nz>
> wrote in comp.lang.c++:
>[color=green]
> > Hi All,
> > I tried to compile the following line:
> > pair<long, ulong> cr3(make_pair(-2147483648L, 2147483647));[/color]
>
> Replace -2147483648L with (-2147483647 - 1)[/color]

If he really wants the minimum long and maximum ulong variables
he really should use numeric_limits min and max.