signed vs unsigned

[LuB]

This isn't a C++ question per se ... but rather, I'm posting this bcs I
want the answer from a C++ language perspective. Hope that makes sense.

I was reading Peter van der Linden's "Expert C Programming: Deep C
Secrets" and came across the following statement:

"Avoid unnecessary complexity by minimizing your use of unsigned types.
Specifically, don't use an unsigned type to represent a quantity just
because it will never be negative (e.g., "age" or "national_debt" )."

Admittedly, I minimize comments in my code. I use them when necessary
but try to limit them to one or two lines. I just don't like their
aesthetic affect in the source. I find the code much harder to read
littered with paragraphs of explanations.

I find the code easier to read when broken up with appropriate newlines
and small, short comments acting as headings.

So - that effectually means that I try my darndest to write
self-describing code. Shorter functions, self-explanatory names for
functions and variable names, etc. Sometimes exceessive commenting is
necessary, but as a whole, I tend to avoid it.

I'm really enjoying Peter's book, but I find this comment hard to
swallow considering that if an age or array index can never be negative
- I would want to illustrate that with an apporpriate choice of type -
namely, unsigned int.

Am I in the minority here? Is my predilection considered poor style?

I guess, from the compiler's standpoint ... using int everywhere is
more portable ... since comparison's against unsigned int can vary
between K&R and ANSI C.

I'm not incurring some type of performance penalty for such decisions
am I?

Thanks in advance,

-Luther

[Bob Hairgrove]

On 21 Feb 2006 08:58:23 -0800, "LuB" <lu*********@ya hoo.com> wrote:

I'm really enjoying Peter's book, but I find this comment hard to
swallow considering that if an age or array index can never be negative
- I would want to illustrate that with an apporpriate choice of type -
namely, unsigned int.

Am I in the minority here?
Hopefully not!
Is my predilection considered poor style?

Absolutely not!

The key to dealing with signed vs. unsigned is not to mix them, if
possible, in comparisons. Be especially wary of comparing an unsigned
counter value to 0 while decrementing the counter.

--
Bob Hairgrove
No**********@Ho me.com

[Cory Nelson]

Like you said, marking a type as "unsigned" if for nothing else is an
easy documentation for other developers that it will never be negative.
I havn't read his stuff but I can't imagine what complexities he is
talking about.

Performance differences depend largly on your architecture. On AMD64,
division/modulus are faster when using unsigned types. Conversion to
floating point is faster with signed types. Addition/subtraction are
the same.

[roberts.noah]

LuB wrote:

I'm really enjoying Peter's book, but I find this comment hard to
swallow considering that if an age or array index can never be negative
- I would want to illustrate that with an apporpriate choice of type -
namely, unsigned int.

The only reason that I can think of that you might want to not use
'unsigned' is if the assumption that it will never be negative might
change. However, most times you are better off with the assumption and
the protection of the unsigned type and then change it later if you
have to. Minimize dependencies on the type so that it is easier to do.

The great thing about unsigned is if the value can't be negative and
you use signed then you always have to check it. Simply defining the
type as unsigned gets rid of all that as well as documenting your
domain.

[Tomás]

LuB posted:

This isn't a C++ question per se ... but rather, I'm posting this bcs I
want the answer from a C++ language perspective. Hope that makes sense.

I was reading Peter van der Linden's "Expert C Programming: Deep C
Secrets" and came across the following statement:

"Avoid unnecessary complexity by minimizing your use of unsigned types.
Specifically, don't use an unsigned type to represent a quantity just
because it will never be negative (e.g., "age" or "national_debt" )."

Admittedly, I minimize comments in my code. I use them when necessary
but try to limit them to one or two lines. I just don't like their
aesthetic affect in the source. I find the code much harder to read
littered with paragraphs of explanations.

I find the code easier to read when broken up with appropriate newlines
and small, short comments acting as headings.

So - that effectually means that I try my darndest to write
self-describing code. Shorter functions, self-explanatory names for
functions and variable names, etc. Sometimes exceessive commenting is
necessary, but as a whole, I tend to avoid it.

I'm really enjoying Peter's book, but I find this comment hard to
swallow considering that if an age or array index can never be negative
- I would want to illustrate that with an apporpriate choice of type -
namely, unsigned int.

Am I in the minority here? Is my predilection considered poor style?

I guess, from the compiler's standpoint ... using int everywhere is
more portable ... since comparison's against unsigned int can vary
between K&R and ANSI C.

I'm not incurring some type of performance penalty for such decisions
am I?

Thanks in advance,

-Luther

My first rule is to write "const" wherever I can.
(except for return types).

My second rule is to write "unsigned" wherever I can.
Thus I'll write:

unsigned GetDogAge(unsig ned const age)
{
return age * 7;
}

Or alternatively re-use the parameter variable:

unsigned GetDogAge(unsig ned age)
{
return age *= 7;
}
-Tomás

[Daniel T.]

In article <11************ **********@f14g 2000cwb.googleg roups.com>,
ro**********@gm ail.com wrote:

The great thing about unsigned is if the value can't be negative and
you use signed then you always have to check it. Simply defining the
type as unsigned gets rid of all that as well as documenting your
domain.

And the bad thing about unsigned is that if code would otherwise make
the value negative, you can't check it. IE

void foo( unsigned s ) {
// at this point s == 4294966272
// is it an error (s came in as -1024) or
// does the client really want us to deal with that number?
}

Bjarne Stroustrup says, "The unsigned integer types are ideal for uses
that treat storage as a bit array. Using an unsigned instead of an int
to gain one more bit to represent positive integers is almost never a
good idea. Attempts to ensure that some values are positive by declaring
variables unsigned will typically be defeated by the implicit conversion
rules."

--
Magic depends on tradition and belief. It does not welcome observation,
nor does it profit by experiment. On the other hand, science is based
on experience; it is open to correction by observation and experiment.

[roberts.noah]

Tomás wrote:

Or alternatively re-use the parameter variable:

unsigned GetDogAge(unsig ned age)
{
return age *= 7;
}

Performs an unnecissary and unused assignment as age is automatic and
will be gone after return.

[forkazoo]

LuB wrote:

This isn't a C++ question per se ... but rather, I'm posting this bcs I
want the answer from a C++ language perspective. Hope that makes sense.

I was reading Peter van der Linden's "Expert C Programming: Deep C
Secrets" and came across the following statement:

"Avoid unnecessary complexity by minimizing your use of unsigned types.
Specifically, don't use an unsigned type to represent a quantity just
because it will never be negative (e.g., "age" or "national_debt" )."
<snip> -Luther

Well, it is a style issue, so many people will probably disagree with
me. They are probably all right, and I would still be able to respect
them :)

That said, I personally use signed types almost all the time, even if
something should never be negative. Every once in a while, I make a
horribly stupid error in something like a file loading function.
Suppose an object can have zero or more child objects. If my loader
returns an object that claims to have -1024 children, then I know I've
done something wrong, and it can be easier to track down bugs that
compile and don't crash. If it just claims that there are a large
positive number of children, it's not as easy to catch the error
condition. There is even the wildly unlikely possibility that there is
an error due to a hardware fault like bad RAM. (Though, the problems
are almost always caused by me! Many people who are better programmers
than me may find that hardware accounts for a greater percentage of
problems than I do :)

Also, I use negative values as intentional error codes and special
cases. Some people consider this horrible style. I can respect that.
But, for a lot of the things I do, it is the quickest, easiest,
simplest, and clearest way to have a recoverable error. So, my
hypothetical object loading function might return an object which
claims -1 children if it failed to open the file, -2 if it failed to
parse the file, -3 if the file contained invalid information, etc. I
know, exceptions are probably better for most of these things, but my
personal style is to write C++ that looks a lot like C, and uses
occasional C++ features. It's just more inline with the way I think
about the problems.

Also, by always using signed types, I can avoid comparisons between
signed and unsigned. It is also generally easier to catch overflow.
After all, the national debt might never be negative, but it certainly
might exceed MAX_INT on some systems! :)

I tend to work alone on personal projects. So, the most important
thing for me is that my personal coding style is readable - to me.
Feel free to strongly disagree with my style.

[Neil Cerutti]

On 2006-02-21, Tomás <NU**@NULL.NULL > wrote:

My first rule is to write "const" wherever I can.
(except for return types).

My second rule is to write "unsigned" wherever I can.
I don't agree with that rule.
Thus I'll write:

unsigned GetDogAge(unsig ned const age)
{
return age * 7;
}

What do you expect to happen if a client passes in an negative int?

The argument is not in the domain, yet the error has been rendered
impossible to detect or recover from.

--
Neil Cerutti

[Alf P. Steinbach]

* Neil Cerutti:

On 2006-02-21, Tomás <NU**@NULL.NULL > wrote:

My first rule is to write "const" wherever I can.
(except for return types).

My second rule is to write "unsigned" wherever I can.

I don't agree with that rule.

Thus I'll write:

unsigned GetDogAge(unsig ned const age)
{
return age * 7;
}

What do you expect to happen if a client passes in an negative int?

The argument is not in the domain, yet the error has been rendered
impossible to detect or recover from.

I don't disagree with your viewpoint regarding using or not using
unsigned whenever possible; I think both are valid viewpoints, and as
with indentation the main thing is to be consistent in one's choices.

However, I disagree with your reason!

With the unsigned argument a validity test might go like

assert( age < 200 ); // unsigned validity test.

With a signed argument the test might go like

assert( age >= 0 ); // signed validity test.
assert( age < 200 ); // more signed validity test.

Now, first of all that demonstrates the "impossible to detect" is simply
incorrect, and second, in my view it demonstrates a slight superiority
for unsigned in this particular case, with respect to validity testing.

Cheers,

- Alf

--
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Q: Why is it such a bad thing?
A: Top-posting.
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