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]

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]

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.

 

[Mike Wahler]

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]

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
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[Ron Natalie]

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.