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By Blog Staff | Oct 13, 2014 10:03 AM | Tags: None
Two regular expressions can go a long way.
Lightweight C++ options parser
by Jarryd Beck
From the article:
Using the new C++11 regular expressions, command line option parsing becomes trivial. I wrote a lightweight command line options parser because I was unsatisfied with all of the other libraries out there...
By Blog Staff | Oct 13, 2014 08:59 AM | Tags: None
Today on the Codexpert blog:
User-defined literals
by Marius Bancila
From the article:
The C++11 standard introduced the possibility to create user-defined literals, that are basically built-in type literals (
integer,float,charor string) followed by a used-defined suffix. User-defined literals enable the creation of new objects based on the built-in literal value and the applied user-defined suffix.auto temp = 77_fah; // 77 Fahrenheit degrees = 25 Celsius degrees auto size = 1_KB; // 1 kilobyte = 1024 bytes auto emp = "marius"_dev; // a user defined type Developer
By Blog Staff | Oct 13, 2014 05:41 AM | Tags: None
Fresh over the weekend, and in this morning's Standardization feed:
N4128: Ranges for the Standard Library
by Eric Niebler
From the article:
Eleven months ago, I began work on an updated range library for modern C++. Yesterday, I submitted a proposal to the C++ standardization committee to add ranges to the Standard Library. The proposal presents a vision for a future Standard Library that is familiar and yet more powerful, more usable, and more efficient than today’s.
My goal is nothing less than to change how C++ programmers write code. Seriously.
By Blog Staff | Oct 10, 2014 07:14 AM | Tags: None
Overload 123 is now available. It contains the following C++-related articles, and more:
[No pun intended. --Ed.] How do you return a default value given a condition? Malcolm Noyes presents solutions using older and newer C++ techniques.
Debugging any program can be time consuming. Sergey Ignatchenko and Dmytro Ivanchykhin extend their mathematical model to consider the effect of assertions.
The Visitor pattern can involve non-local boilerplate code. Robert Mill and Jonathan Coe present an inline VISITOR in C++.
By Blog Staff | Oct 9, 2014 08:41 AM | Tags: basics
Quick A: Because it performs worse than C++98 for common types like string and vector. The preferred way to optimize for rvalues is to add a && overload.
Fresh on SO:
Why is value taking setter member functions not recommended in Herb Sutter's CppCon 2014 talk (Back to Basics: Modern C++ Style)?
In Herb Sutter's CppCon 2014 talk Back to Basics: Modern C++ Style he refers on slide 28 (a web copy of the slides are here) to this pattern:
class employee { std::string name_; public: void set_name(std::string name) noexcept { name_ = std::move(name); } };He says that this is problematic because when calling
set_name()with a temporary, noexcept-ness isn't strong (he uses the phrase "noexcept-ish").Now, I have been using the above pattern pretty heavily in my own recent C++ code mainly because it saves me typing two copies of set_name() every time -- yes, I know that can be a bit inefficient by forcing a copy construction every time, but hey I am a lazy typer. However Herb's phrase "This noexcept is problematic" worries me as I don't get the problem here: std::string's move assignment operator is noexcept, as is its destructor, so set_name() above seems to me to be guaranteed noexcept. I do see a potential exception throw by the compiler before set_name() as it prepares the parameter, but I am struggling to see that as problematic.
Later on on slide 32 Herb clearly states the above is an anti-pattern. Can someone explain to me why lest I have been writing bad code by being lazy?
By Blog Staff | Oct 7, 2014 08:40 AM | Tags: basics
Quick A: Because they reduce code duplication, and so make code more readable and maintainable.
Recently on SO:
Why did C++11 introduce delegating constructors?
I cannot understand what the use is of delegating constructors. Simply, what cannot be achieve without having delegating constructors?
It can do something simple like this
class M { int x, y; char *p; public: M(int v) : x(v), y(0), p(new char [MAX]) {} M(): M(0) {cout<<"delegating ctor"<<endl;} };But I don't see it, is it worth introducing a new feature for such a simple thing? May be I couldn't recognize the important point. Any idea?
By Blog Staff | Oct 7, 2014 12:34 AM | Tags: experimental
New in Eric's series on ranges for C++:
Ranges in C++: Counted Iterables and Efficiency
by Eric Niebler
From the article:
I’ve been hard at work fleshing out my range library and writing a proposal to get range support into the standard. That proposal describes a foundational range concept: Iterable. An Iterable is anything we can pass to
std::begin()andstd::end()to get an Iterator/Sentinel pair. Sentinels, as I described here earlier this year, make it possible for the Iterable concept to efficiently describe other kinds of ranges besides iterator pairs.The three types of ranges that we would like the Iterable concept to be able to efficiently model are:
- Two iterators
- An iterator and a predicate
- An iterator and a count
The Iterator/Sentinel abstraction is what makes it possible for the algorithms to handle these three cases with uniform syntax. However, as Sean Parent pointed out here, the third option presents challenges when trying to make some algorithms optimally efficient. Back in February, when Sean offered his criticism, I promised to follow up with a blog post that justified the design. This is that post.
By Blog Staff | Oct 5, 2014 09:26 PM | Tags: intermediate
Quick A: Yes.
A classic on SO, just re-asked yesterday:
When to use std::begin and std::end instead of container specific versions
Are there any general preferences or rules that explain when container specific versions of
beginandendshould be used instead of free functionsstd::beginandstd::end?It is my understanding that if the function is a template whereby the container type is a template parameter then
std::beginandstd::endshould be used, i.e.:template<class T> void do_stuff( const T& t ) { std::for_each( std::begin(t), std::end(t), /* some stuff */ ); }What about in other scenarios such as a standard / member function where the type of container is known? Is it still better practice to use
std::begin(cont)andstd::end(cont)or should the container's member functionscont.begin()andcont.end()be preferred?Am I correct in assuming that there is no benefit in performance by calling
cont.end()overstd::end(cont)?
By Blog Staff | Oct 4, 2014 12:03 AM | Tags: None
ACCU 2015 is now putting together its program, and they want you to speak on C++. ACCU has long had a strong C++ track, though it is not a C++-only conference. If you have something to share, check out the call for papers.
Call for Papers
ACCU 2015
We invite you to propose a session for this leading software development conference...
The Call for Papers lasts 5 weeks and will close at midnight Wednesday 5th November 2014. Remember, remember, the 5th of November...
By Meeting C++ | Oct 3, 2014 07:49 AM | Tags: performance intermediate efficiency c++14 c++11 boost basics
I've written down some basic thinking on new and new standards:
Insights into new and C++
by Jens Weller
From the article:
Every now and then, I've been thinking about this. So this blogpost is also a summary of my thoughts on this topic, dynamic memory allocation and C++. Since I wrote the blog entries on smart pointers, and C++14 giving us make_unique, raw new and delete seem to disappear from C++ in our future code...