Re: Unsignedness of std::size_t
Kaba wrote:
Here you can find an article "Signed and unsigned types in interfaces"
by Scott Meyers:
http://www.aristeia.com/publications_frames.html
After reading that article it should be clear why it is not a good idea
to use unsigned types just to reinforce a positiveness precondition to a
function parameter. Yet the standard library does just this by using
std::size_t which is unsigned.
This article is from the year 1995, three years before the 1998
standard. Why is the std::size_t still unsigned?
To be honest, I disagree with that article. The point is that this article
propagates using types so that
int n = strlen(p);
works. However, you can't do that reliably without too much fuss. The point
is that the above code is broken in several ways:
1. strlen() returns a size_t. This is the first and foremost fault in this
code, because those typedefs exist for the exact reason that you can refer
to them. Further, they are guaranteed to match the output of strlen(), so
using them you will never have problems due to faulty conversions.
2. If you compile that, any compiler worth its name will give you a warning
because the target type differs in signedness and possibly size from the
correct type. If you choose to ignore the warning, you do so on your own. I
for one wouldn't sacrifice functionality and performance for programmers
that are too stupid to read and understand warnings.
Now, concerning underflows in arithmetic, this doesn't change anything. If
get your computations wrong, they are wrong. A good library might flag the
error so it gets caught earlier[1], but it simply can't solve programming
errors in code it doesn't control. Further, I also think it shouldn't,
because that would come at a cost for programmers that write correct
programs.
Uli
[1] e.g. malloc() could print a debug message when someone tries to reserve
more memory than ever possible on a certain platform, but that is not
simply 2^31 for 32 bit platforms, some allow up to 3GiB for user processes.
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