loop for all values of ushort ports using ushort index .... with caution.

[pete]

pete <[email protected]> wrote:

[about:]

unsigned short port = 0;
do { [...]
} while (++port != 0);
It's undefined if INT_MAX equals USHRT_MAX.

while ((port += 1u) != 0);

That won't do what you want,
if UINT_MAX is greater than USHRT_MAX.

Would you care to explain?
Yes.

The loop (in this sub-thread) was
meant to iterate over all unsigned values.

No, it wasn't.
My comment "It's undefined if INT_MAX equals USHRT_MAX.",
refers to the increment operator causing a promotion
of type unsigned short, to type int.
(1 + INT_MAX) is undefind.
(++port) means exactly the same thing as (port = port + 1).

Peter Nilsson addressed that issue by replacing
++port with (port += 1u), thus causing the promotion to be to
type unsigned.
(1 + UINT_MAX) *is* defined as zero.
But then, as I said, the loop will do more
than just all of the values for unsigned short
if UINT_MAX is greater than USHRT_MAX.

 

[Peter Nilsson]

Peter Nilsson wrote:
unsigned short port = 0;
do { [...]
} while (++port != 0);

It's undefined if INT_MAX equals USHRT_MAX.

while ((port += 1u) != 0);

That won't do what you want,
if UINT_MAX is greater than USHRT_MAX.

... the loop will do more
than just all of the values for unsigned short
if UINT_MAX is greater than USHRT_MAX.

How so? The type of port, and therefore (port += 1u),
is unsigned short.

(unsigned short) (USHRT_MAX + 1u) == 0

If port has the value USHRT_MAX in the do/while body,
then it will have the value 0 on evaluation of the
conditional expression, hence the loop will break.

 

[pete]

pete wrote:
Peter Nilsson wrote:
[about:]
unsigned short port = 0;
do {
[...]
} while (++port != 0);

It's undefined if INT_MAX equals USHRT_MAX.

while ((port += 1u) != 0);

That won't do what you want,
if UINT_MAX is greater than USHRT_MAX.

... the loop will do more
than just all of the values for unsigned short
if UINT_MAX is greater than USHRT_MAX.

How so? The type of port, and therefore (port += 1u),
is unsigned short.

(unsigned short) (USHRT_MAX + 1u) == 0

If port has the value USHRT_MAX in the do/while body,
then it will have the value 0 on evaluation of the
conditional expression, hence the loop will break.

You're right.
I'm wrong.