Ranges and Iterators for numerical problems

By Meeting C++ | Feb 12, 2015 09:29 AM | Tags: performance intermediate c++11 boost

A guest blog post by Karsten Ahnert at Meeting C++ as a follow up of his talk!

Ranges and Iterators for numerical problems

by Karsten Ahnert

From the article:

In this blog post I am going to show some ideas how one can implement numerical algorithms with ranges. Examples are the classical Newton algorithm for finding the root of a function and ordinary differential equations. The main idea is to put the main loop of the algorithm into range such that the user can...

ODB C++ ORM 2.4.0 Released, Adds Bulk Operations Support

By Boris Kolpackov | Feb 11, 2015 11:55 AM | Tags: None

ODB C++ ORM 2.4.0 Released, Adds Bulk Operations Support

by Boris Kolpackov

ODB is an open source object-relational mapping (ORM) system for C++. It allows you to persist C++ objects to a relational database without having to deal with tables, columns, or SQL and without manually writing any of the mapping code.

Major new features in this release:

• Support for bulk operations in Oracle and SQL Server. Bulk operations can be used to persist, update, or erase a range of objects using a single database statement execution which often translates to a significantly better performance.
• Ability to join and load one or more complete objects instead of, or in addition to, a subset of their data members with a single SELECT statement execution (object loading views).
• Support for specifying object and table join types in views (LEFT, RIGHT, FULL, INNER, or CROSS).
• Support for calling MySQL and SQL Server stored procedures.
• Support for defining persistent objects as instantiations of C++ class templates.

A more detailed discussion of these features can be found on the blog. For the complete list of new features in this version see the official release announcement.

ODB is written in portable C++ (both C++98/03 and C++11 are supported) and you should be able to use it with any modern C++ compiler. In particular, we have tested this release on GNU/Linux (x86/x86-64/ARM), Windows (x86/x86-64), Mac OS X (x86/x86_64), and Solaris (x86/x86-64/SPARC) with GNU g++ 4.2.x-5.x, MS Visual C++ 2005, 2008, 2010, 2012, and 2013, Sun Studio 12u2, and Clang 3.x.

The currently supported database systems are MySQL, SQLite, PostgreSQL, Oracle, and SQL Server. ODB also provides optional profiles for Boost and Qt, which allow you to seamlessly use value types, containers, and smart pointers from these libraries in your persistent classes.

More information, documentation, source code, and pre-compiled binaries are available on the project's page.

How do I write complex initialization?--Stack Overflow

By Adrien Hamelin | Feb 11, 2015 11:21 AM | Tags: intermediate c++11

Quick A: Initialize it using a lambda that’s invoked immediately.

Recently on SO:

Best practice for declaring variable without initialising it, so auto is unavailable

I want to declare two variables of the same type, and have the compiler figure out the types. However I don't want to initialise one of the variables until later. I don't think I can use auto here, so what's the best option?

std::vector<int> v;

// `start` and `end` should be the same type
auto start = v.begin();
??? end;

// complicated code to assign a value to `end` (i.e. putting
// the code in a function or using ?: is not practical here) 
if (...) {
    end = ...;
} else {
    end = v.end();
}

What's the best way to tell the compiler that end should be the same type as start, but without having to initialise the variable?

auto start = v.begin(), end;  // Doesn't work, `end` has to be initialised
decltype(start) end;          // Does work, but not sure if it's best practice

Update

A couple of comments have suggested ways that would work in certain situations, so I am clarifying my situation here:

std::vector<int> v;
int amount = 123;

// `start` and `end` should be the same type
auto start = v.begin();
??? end;

// code to assign a value to `end`
if (amount) {
    end = start + amount;
    amount = 0;
} else {
    end = v.end();
}

I believe a lamda function would be trickier here, because amount is being reset to 0 after end is calculated, so in a lamda function that calculates a value for end, amount = 0 would have to come after the return statement. The only option would be to create more local variables, which would incur an (admittedly tiny) performance penalty.

The Rule of Zero revisited: The Rule of All or Nothing--Arne Mertz

By Adrien Hamelin | Feb 11, 2015 11:17 AM | Tags: c++11 basics

In this article you will find a new rule of thumb:

The Rule of Zero revisited: The Rule of All or Nothing

by Arne Mertz

From the article:

In 2012, Martinho Fernandes coined the Rule of Zero in a blog post. In 2014, Scott Meyers wrote a blog post about a concern with that rule and proposed a Rule of Five Defaults.

Back then, I had written a small comment on Scott’s post that deserves some further elaboration. In this post I am going to wrap up my thoughts about the two posts and propose a “Rule of All or Nothing”...

the asynchronous library - Christophe Henry @ Meeting C++ 2014

By Meeting C++ | Feb 11, 2015 10:24 AM | Tags: performance parallelism intermediate experimental c++11

A new video from Meeting C++ 2014:

the asynchronous library

by Christophe Henry

From the talk description:

An infrastructure library on which Boost Meta State Machine can build. This will be provided by the Asynchronous library: Active Objects, proxies, threadpools, parallelization algorithms, work-stealing, distributed programming...

2015-02 mid-meeting mailing available

By Blog Staff | Feb 11, 2015 09:49 AM | Tags: None

The 2015-02 mailing of new standards papers is now available.

NOTE: A number of these papers have already been publicized on this blog. This is the complete list including ones not previously publicized.

CppCon 2014 How HHVM Uses Modern C++ for Fun and Profit (Literally)--Drew Paroski

By Adrien Hamelin | Feb 11, 2015 08:00 AM | Tags: intermediate

While we wait for CppCon 2015 in September, we’re featuring videos of some of the 100+ talks from CppCon 2014. Here is today’s feature:

How HHVM Uses Modern C++ for Fun and Profit (Literally)

by Drew Paroski

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

HHVM is a just-in-time compiler for PHP used by Facebook to serve billions of requests each day. This talk will give a quick overview of HHVM's history and architecture, followed by a deep dive into what made C++ the language of choice for writing HHVM.

C++ hits a sweet spot between performance and control on one end, and safety, maintainability, and convenience on the other.

The topics we’ll cover will include:
how to call into generated machine code from C++;
taking advantage of C++'s power to control "unsafe" details with memory including how memory is allocated, field size and layout, unions, reinterpret_casts, bit-stealing;
integrating generated machine code with C++ exception handling and C++ profiling tools;
leveraging templates and using the X Macro technique to improve performance and maintainability;
and taking advantage of new C++11 features like unrestricted unions and move constructors.
Finally, we'll go over some obstacles we encountered such as generating machine code that calls C++ virtual methods, and how C++'s superb flexibility allowed us to work around these obstacles.

Call for Papers: C++ track at NDC Oslo 2015, June 17-19

By Olve Maudal | Feb 10, 2015 01:09 PM | Tags: oslo norway conference cfp

There was a lot of interest for the very strong C++ track that we hosted at the NDC conference in Oslo last summer. Here is a brief summary of the event, including links to the videos we recorded.

We are repeating the success this year, June 17-19. A few big C++ names has already been signed up, but there is still available slots in the agenda. If you would like to be part of the C++ track this year, please submit your proposal soon.

Call For Papers for NDC Oslo 2015

The CFP closes February 15.

Desired compile-time failures--Andrzej Krzemieński

By Adrien Hamelin | Feb 10, 2015 08:51 AM | Tags: intermediate c++11

Sometimes, an error is what we want:

Desired compile-time failures

by Andrzej Krzemieński

From the article:

However, even though [not introducing breaking changes] works in most of the cases, I believe that this criterion of a “safe addition” is not technically correct, as it fails to take into account an important fact: failure to compile certain programs is a useful, important feature, and if these programs suddenly start to compile, it can cause harm. In this post we will go through the cases where compile-time failure is considered a useful feature...

GCC5 and the C++11 ABI--rhjason

By Adrien Hamelin | Feb 10, 2015 08:24 AM | Tags: c++11 advanced

A new article of interest for library developers:

GCC5 and the C++11 ABI

by rhjason

From the article:

The GNU C++ team works hard to avoid breaking ABI compatibility between releases, including between different -std= modes. But some new complexity requirements in the C++11 standard require ABI changes to several standard library classes to satisfy, most notably to std::basic_string and std::list. And since std::basic_string is used widely, much of the standard library is affected...