Today, Vikram Ojha asked via email:

I was just thinking why we removed “int” as default return type from C++ which was there in our traditional C type. Why we made such changes, is it to make language more safer?

Short answer: Because it’s ‘inherently dangerous’ in the words of the C committee.

For C++, see D&E (The Design and Evolution of C++) index “implicit int” which takes you to section 2.8.1. For C, see the C99 Rationale section 6.7.2 — interestingly, you can’t search for “implicit int” because that term isn’t used — this is where the string to search for is “inherent danger” :).

Cribbing from Bjarne’s writeup, “implicit int” was removed some 20 years ago for several reasons, including code clarity and in additional avoiding special cases, to simplify C++ code and/or the C++ grammar.

For example, what does this mean?

void f(const T);

In modern C++, it can mean only that f has a const parameter of type T that is unnamed.

If we had implicit int, this would be less obvious: Could it also be a const parameter of type int named T?

There are a number of other cases where just omitting the type, with the meaning that it’s a certain fixed type, makes the grammar and/or the program harder to think about than it should be. So the ability to do that was removed in both C and C++.

[Edit: I really like the ‘range of values’ several commenters proposed. We do need something like that in the standard library, and it may well come in with ranges, but as you can see there are several simple ways to roll your own in the meantime, and some third-party libraries have similar features already.]

Today a reader asked the following question:

So I’ve been reading all I can about c++11/c++14 and beyond when time permits.  I like auto, I really do, I believe in it.  I have a small problem I’m trying to decide what to do about.  So in old legacy code we have things like this:

for (int i = 0; i < someObject.size(); i++) { … }

For some object types size might be unsigned, size_t, int, int64_t etc…

Is there a proper way to handle this generically with auto?  The best I could come up with is:

auto mySize = someObject.size();

for (auto i = decltype(mySize){0}; i < mySize; i++) { … }

But I feel dirty for doing it because although it actually is very concise, it’s not newbie friendly to my surrounding coworkers who aren’t as motivated to be on the bleeding edge.

Good question.

First, of course, I’m sure you know the best choice is to use range-for where that’s natural, or failing that consider iterators and begin()/end() where auto naturally gets the iterator types right. Having said that, sometimes you do need an index variable (including for performance) so I’ll assume you’re in that case.

So here’s my off-the-cuff answer:

• If this isn’t in a template, then I think for( auto i = 0; etc. is fine, and if you get a warning about signed/unsigned mismatch just write for(auto i = 0u; etc. This is all I’ve usually needed to do.

• If this is truly generic code in a template, then I suppose for( auto i = 0*mySize; etc. isn’t too bad – it gets the type and it’s not terribly ugly. Disclaimer: I’ve never written this, personally, as I haven’t had a need (yet). And I definitely don’t know that I like it… just throwing it out as an idea.

But that’s an off-the-cuff answer. Dear readers, if you know other/better answers please tell us in the comments.

Consider this program fragment:

std::vector<int> v = { 0, 0 };
int i = 0;
v[i++] = i++;
std::cout << v[0] << v[1] << endl;

My question is not what it might print under today’s C++ rules. The third line runs afoul of two different categories of undefined and unspecified behavior.

Rather, my question is what you would like the result to be. Please let me know.

(this is an echo of what I also just posted on isocpp.org)

I wanted to add a few more things to my meeting trip report. I updated the trip report in-place, but for those who want to see the “diffs” I’ll also post just the new parts here as a standalone post:

There were 106 experts at this meeting, officially representing 7 nations. This meeting saw a recent-record number of papers, including over 120 in the pre-meeting mailing.

In addition to the other things I mentioned, we also approved several other interesting changes, including the following highlights:

• Adopted N4230, which allows nested namespace definitions like namespace A::B::C { } as a convenient shorthand for namespace A { namespace B { namespace C { } } }.
• Adopted N3922, which fixes the most common pitfall with auto and {}, so that auto x{y}; now deduces the sane and expected thing, namely the type of y. Before this, it deduced initializer_list which was unfortunate and surprising. So, fixed.
• Adopted N4086, which removes trigraphs. Yes, we removed something from C++… and something that was inherited from C! But wait, there’s more…
• Adopted N4190, and actually removed (not just deprecated) several archaic things from the C++ standard library, including auto_ptr, bind1st/bind2nd, ptr_fun/mem_fun/mem_fun_ref, random_shuffle, and a few more. Those are now all removed from the draft C++17 standard library and will not be part of future portable C++.

We also did work and made progress on a lot of other proposals, including modules. See the pre-meeting mailing for details about papers considered at this meeting.

I just posted my ISO C++ meeting trip report over on isocpp.org covering our meeting in Urbana-Champaign earlier this month.

The ISO C++ committee is shipping more work sooner via concurrent Technical Specifications, but it’s still fairly new to find ourselves doing so much work that the “new normal” is to issue an international ballot from every ISO C++ meeting. This time, we have four ballots coming out of this meeting — the first (of two) ballots for the Transactional Memory TS, the final ballots for the Library Fundamentals TS and the Parallelism TS, and a new work item for C++17 since this was the first meeting of the C++17 era.

Oh, and we had evening sessions. Did I mention evening sessions? Five nights’ worth.

Now, two weeks later, I’m almost caught up on sleep.

Almost.

But what a blast. I’m looking forward to the next few smaller meetings over the winter, and the next full one in May.

Today my team was part of the Visual Studio 2015 Preview announcement, and it’s nice to be able to share that Visual Studio is now going to support targeting Android and soon iOS, using the Clang compiler, from right inside VS. This is in addition to continued conformance and other improvements in our own VC++ compiler for targeting Microsoft platforms.

I recorded an 8-minute video about Visual C++’s conformance improvements in our existing compiler that you can get now in the Preview available today, and why using a single source code base in C++ built using VC++ to target Windows/WP and also Clang/LLVM to target Android and iOS is a hot ticket right now. The Resources slide at the end includes links to two CppCon videos I hope you’ll check out if you haven’t already.

I hope you enjoy the news, and the Preview.

Also, my CppCon talks are all up on the CppCon YouTube channel. You can find them here:

• Back to the Basics! Essentials of Modern C++ Style: Loops, pointers and references, smart pointers, variable declarations, and parameter passing
• Lock-Free Programming (or, Juggling Razor Blades), Part 1: Lazy initialization with DCL vs. call_once vs. function local statics, and lock-free mailbox algorithms
• Lock-Free Programming (or, Juggling Razor Blades), Part 2: Lock-free linked lists, the ABA problem, and atomic smart pointers

I hope you find them useful.

While we were both at CppCon last month and had cameras around, Brian Overland interviewed me for InformIT. The video just went up a couple of days ago. You can find it here.

If you’ve seen my interviews before, the first 14 minutes is stuff you’ve heard before, but I think you’ll find the last five minutes starting at 14:23 to be interesting new material.

CppCon was a blast. I can’t wait till next year.

But there’s something coming up sooner than that: In two weeks, Scott and Andrei and I will be holding the C++ and Beyond 2014 “Road Show” in Stuttgart, Germany.

The key to this event is not new material, but a new location. Whereas all other C&B’s have been in North America, this is the first time ever that Scott and Andrei and I are doing an event together in Europe. That’s exciting! (At least for us.) If you’ve been to C&B you will have seen most of this material before, but if you haven’t been able to get to C&B until now you may find it convenient to have the event be more local to European attendees. The talks are all talks we’ve given at C&B before, but there will be updates.

Scott seems to be looking forward to a debate with me about parameter passing. I’m glad he thinks I’m “seeing more reason than [I] used to, (i.e., having moved closer to [Scott’s] point of view)” – by which he means that he has moved closer to my point of view. :) Should be fun! The boring truth, as I presented at CppCon on Friday, is that everyone agrees that the default parameter passing rules are the same as C++98… <gd&r> and let the games begin!

I just posted my CppCon trip report over at isocpp.org.

I’ll repeat just the last part here:

Huge thanks again to the 150+ speakers, planners, and volunteers without whom this wonderful “C++ festival” (as several people spontaneously called it) would not have been possible. I had guardedly high hopes for the event, but I think it exceeded all our expectations. This was the most exciting and enlightening week I’ve experienced in my 20 years of C++, and I’m still catching my breath. I can’t wait until September 2015.

Here are a few pics I and others took. You’ll find more on Twitter tagged #cppcon.

Mark Maimone of NASA and Mars Rover fame.

Bjarne taking questions after his talk.

“We’re sold out of A Tour of C++ again… how about this instead?” [photo credit: Artur Laksberg]

[photo credit: Artur Laksberg]

[photo credit: Artur Laksberg]

Walter Brown speaking in one of the six concurrent breakout sessions.

Jon Kalb speaking in one of the other rooms.

Possibly the youngest attendee? [photo credit: Artur Laksberg]

Accessibility and community.

Yup. Modern C++.

View from the CppCon balcony before diving into more evening sessions.

So long, Meydenbauer Center… see you next year! [photo credit: Hyrum Wright]