Re: What is your opinion about unsigned int u = -2 ?

Thiago Adams <thiago.adams@gmail.com> writes:

Em 8/2/2024 10:31 PM, Keith Thompson escreveu:

Thiago Adams <thiago.adams@gmail.com> writes:
[...]

It is interesting to compare constexpr with the existing constant
expression in C that works with integers.Compilers extend to work with
unsigned long long.
constexpr works with the sizes as defined , for instance char.

I'm not sure what you mean by "Compilers extend to work with
unsigned long long.".

>
enum {C = 18446744073709551615 -1 };
//        ~~~~~~~~~~~~~~~~~~~~
//        ^ warning: integer constant is so large that it is unsigned
>
https://godbolt.org/z/K7hzczETP

Since 18446744073709551615 is 2**64-1, it's outside the range of any
signed integer type in typical implementations.  Since unsuffixed
integer constants are of some signed type (since C99), that constant is
likely to cause problems.  You could write 18446744073709551615ull.

That's a rather odd warning.  In C90, an unsuffixed integer constant's
type was the first of (int, long int, unsigned long int) in which its
value would fit.  In C99 and later, an unsuffixed integer constant is of
type int, long int, or long long int, *never* of any unsigned type.
Since 18446744073709551615 exceeds ULLONG_MAX (assuming 64 bits),
apparently gcc treats it as having an unsigned type as an extension.

(My quick experiment indicates that, at least on my system,
18446744073709551615 is of type __int128 and, bizarrely,
18446744073709551616 is of type int with the value 0.  This seems
like a bug.)

This part "shall only have operands that are integer constants"
>
From C23
>
"An integer constant expression132) shall have integer type and shall
only have operands that are
integer constants, named and compound literal constants of integer
type, character constants,
sizeof expressions whose results are integer constants, alignof
expressions, and floating, named,
or compound literal constants of arithmetic type that are the
immediate operands of casts. Cast
operators in an integer constant expression shall only convert
arithmetic types to integer types,
except as part of an operand to the typeof operators, sizeof operator,
or alignof operator."

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */