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]

> I tried to compile the following line:

pair<long, ulong> cr3(make_pair(-2147483648L, 2147483647));

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

Tõnu.

[Ron Natalie]

"Andrew Ward" <an***@ihug.co.nz> wrote in message news:r1**********************@news.xtra.co.nz...

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

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]

In article <3f********@news.infonet.ee>, to**@ids.ee says...

[ ... ]

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

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]

"Tõnu Aas" <to**@ids.ee> wrote in message news:3f********@news.infonet.ee...

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

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

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

-Mike

[Jack Klein]

On Thu, 25 Sep 2003 16:19:33 +1200, "Andrew Ward" <an***@ihug.co.nz>
wrote in comp.lang.c++:

Hi All,
I tried to compile the following line:
pair<long, ulong> cr3(make_pair(-2147483648L, 2147483647));
Replace -2147483648L with (-2147483647 - 1)

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

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++ ftp://snurse-l.org/pub/acllc-c++/faq

[Ron Natalie]

"Jack Klein" <ja*******@spamcop.net> wrote in message news:dm********************************@4ax.com...

On Thu, 25 Sep 2003 16:19:33 +1200, "Andrew Ward" <an***@ihug.co.nz>
wrote in comp.lang.c++:

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

Replace -2147483648L with (-2147483647 - 1)

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