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    Using 'unsigned' (by itself) to declare the 'unsigned int' type is standard in C++. In the current standard: 7.1.5.2 [dcl.simple.type] has a table that identifies each type declaration to the actual type used. That table has a correspondence from 'unsigned' declaration to 'unsigned int' type. lgo algo-sr relsrch fst richAlgo" data-6d5="645feed072ef2">stackoverflow.com › questions › 2099830Unsigned keyword in C++ - Stack Overflow stackoverflow.com › questions › 2099830 Cached

Stroustrup P1491R0 signed/unsigned

1

Doc. No. P1491R0

Date: 2019

02 14

Programming Language C++

Audience: LEWG and EWG

Reply to: Bjarne Stroustrup (bs@ms.com) Don't add to the signed/unsigned mess

Bjarne Stroustrup

Abstract

There are many ways of writing a simple loop. Too many, and we are proposing to add more. My suggestion: don't.

The root problem is that in C and C++ signed and unsigned integers don't mix well. We should begin the

process of minimizing that problem by not adding more opportunities for such mixing.

Please note that th

is is not a suggestion to change the WP. It is an argument for keeping status quo until we are certain we have something better. Loops As an example, I will use a very simple loop that simply zeros out the elements of a vector.

Use a range for:

for (auto& x : v) x=0;

That's the simplest and often the best, but people - many people - like to play with loop variables and

occasionally they actually need to: for (int i = 0; i::size_type I = 0; iAnd more variations. This is too much and offers many opportunities for confusion; we should not add to that.

Now people are proposing [p0330r4] [p1227R1]:

Stroustrup P1491R0 signed/unsigned

2 for (auto i = 0; is ever, people will get confused and - in addition to my examples - use some of the many more variants

that I haven't mentioned.

Workarounds and alternatives

Of course,

some (but not all) compilers warn about common cases: for (int i = 0; iThat is most annoying because most vectors have far fewer than 2 billion elements. In fact, the standard

limits the number of elements of a vector to the largest positive value of its difference type (General

Container Requirements, table 64). This leads people to complain bitterly about C++, especially novices

and people coming to C++ from other languages. New people come to C++ faster than we can teach them to do such basic things differently from what they were used to.

So, people

and organizations ignore those warnings or suppress them, setting a dangerous example for other warnings and causing trouble when you do get a 2B+ vector. False positives do harm.

People also look for alternatives:

for (int i = 0; i < (int)v.size(); ++i) v[i]=0; // use a cast That's unnecessarily verbose, dangerous in the sense that it could be wrong (here, narrowing on some machines), and teaches people to use the terse, general, and error-prone C-style cast.

Here is a variant that does not use a cast:

for (int i = 0, n = v.size(); i < n; ++i ) v[i]=0; // verbose

Such workarounds

avoid warnings (but narrows and converts unsigned to signed). They also make people wonder about the sanity of C++.

In places, people use a helper

function. For example: for (int i = 0; i < elem_count(v); ++i) v[i]=0;

where elem_count() is a function that takes a container or a range and returns a signed value (and hides

the cast).

For many examples, there are alternatives to C-style for-loops. I mentioned the range-for up front, but

algorithms often offer alternatives std:: fill(v.begin(),v.end(),0); std::fill(v,0); // when we get ranges std:: for_each(v.begin(),v.end(),[](int& x){ x=0; });

Stroustrup P1491R0 signed/unsigned

3

Again, try to explain that to a C++ novice. Better still, try to get the point across to a novice for whom

you are not formally a teacher or a Mentor. Or for someone you will never meet. Unless somehow advised otherwise, such people often (typically?) start with for (int i = 0; iActual proposals [p0330r4] proposes to add to the - already confusing - set of suffixes by adding uz and z (or maybe some other letters). We'd have u, U, l, L, z, Z, f, F, and p (has p been formally proposed?) plus

combinations in addition to user-defined suffixes. There are also decimal floating point and soon short

floats. [p1227R1] proposes to change size() in the ranges TS and for span to unsigned (making them bug compatible with the STL) and adding ssize() to all containers and range accessors embeds a type in a function name (and it makes me think of Parseltongue) leaves the wrong solution (IMO) with the better, more established, and simpler name adds a few more cases to the wrong (IMO) solution [P1428R0]

What other types deserves suffixes?

What other types could

"benefit" from similar addition of signed-

type alternatives to current unsigned ones? Are there types for which such additions would offer more

help to programmers that the current proposals for (just) signed and unsigned? I suspect so. The quest

for patches would be open-ended.

For C++, signed sizes and

subscripts are the best solution : make all size()s signed!. That is not perfect, and I don't propose that for C++20, but it is the solution with the least problems and the best

opportunities to catch problems (e.g., contracts and run-time checks) [P1428R0]. We should aim for that

and start gathering facts/data , rather than adding to the problem (e.g., by changing span::size() to be unsigned).

Acknowledgements

Thanks to Peter Dimov, Tony Van Eerd, Peter Sommerlad, Sergey Zubkov, Herb Sutter, and others for constructive comments of a draft of this.

References

[P0330R4] JeanHeyd Meneide and Rein Halbersma: Literal Suffixes for ptrdiff_t and size_t. [p1227R1] Jorg Brown: Signed ssize() functions, unsigned size() functions. [P1227R3] Jorg Brown: http://wiki.edg.com/pub/Wg21kona2019/StrawPolls/p1227r2.htm (the document voted on in Kona). [P1428R0] Bjarne Stroustrup: Subscripts and sizes should be signed . [Carruth,2016] Chandler Carruth: Garbage In, Garbage Out: Arguing about Undefined Behavior with Nasal Demons CppCon 2016 (starting around 40min in).quotesdbs_dbs14.pdfusesText_20
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