Yes, many compilers will give you a warning about comparing signed to
unsigned. You really just shouldn't do it!

If you think about what happens at the hardware level, where the comparison
is basically  a subtraction, you can't properly interpret the flags (C and =
Z
on a PIC) set by the comparison.

-- Bob Ammerman
RAm Systems


-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Electron
Sent: Friday, May 02, 2014 10:43 AM
To: Microcontroller discussion list - Public.; Microcontroller discussion
list - Public.
Subject: [OT] Why on earth??!?


Hello!

a is a signed int and contains -100
b is an unsigned int and contains 500

a<b returns FALSE!!

Why on earth? :P

I can cast b to signed int and get the correct results, but leaving as is
instead the result surprises me a lot, as I have no idea why -100<500 shoul=
d
be false, it's like if the compiler casts a to an unsigned type
automatically (and this was clearly not requested by the programmer).

If we keep them as they are, i.e. the first signed and the second unsigned,
then why should a<b return false???

This is very confusing really.

Now I have to correct all of my code, looking for comparisons between signe=
d
and unsigned ints, and cast both variables to the type I mean. :-/

Is there any other situation I have to be careful about when mixing signed
and unsigned types?

Please do not reply the obvious "generically the use of unsigned types is
not adviceable, why don't you stick with only signed types? you will be muc=
h
safer". THANKS.

Cheers,
Mario

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