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Optimizing C++ Code: Dead Code Elimination -- Jim Hogg

By Blog Staff | Aug 28, 2013 12:29 PM | Tags: intermediate

We keep hearing about C++'s "as if" rule, but what does it really do? Fundamentally, it enables optimizations. A modern compiler never produces an executable that's identical to the program you actually wrote; it produces an equivalent program that's probably a lot better.

Hence Jim Hogg's nice new series on what optimizing compilers do, using Visual C++ as an example. The latest instalment:

Optimizing C++ Code : Dead Code Elimination

by Jim Hogg

From the article:

This post examines the optimization called Dead-Code-Elimination, which I’ll abbreviate to DCE.  It does what it says: discards any calculations whose results are not actually used by the program.

Now, you will probably assert that your code calculates only results that are used, and never any results that are not used: only an idiot, after all, would gratuitously add useless code -- calculating the first 1000 digits of pi, for example, whilst also doing something useful.  So when would the DCE optimization ever have an effect? ...

C++: Polymorphic Cloning and the CRTP (Curiously Recurring Template Pattern)--Katy Coe

By matt | Aug 23, 2013 06:06 AM | Tags: polymorphism intermediate crtp cloning c++11

katy.pngOn CRTP with multi-level inheritance, cloning, and the constructor forwarding problem.

C++: Polymorphic cloning and the CRTP (Curiously Recurring Template Pattern)

by Katy Coe

From the article:

A common problem in C++ occurs when you have an object of an unknown derived type and want to make a copy of it. ...

The solution is to use the commonly-used polymorphic cloning pattern. In this pattern, we define a virtual function -- which we’ll call clone() in this article -- which when called via an object pointer returns a new object of the correct derived type.

Continue reading...

noexcept Destructors -- Andrzej Krzemieński

By Blog Staff | Aug 20, 2013 06:03 PM | Tags: intermediate

A slight change from C++98 to C++11, tightening up destructor semantics. Yes, it's still considered a best practice to never allow an exception to escape from a destructor -- in any language with destructor or Dispose functionality -- and now we have an additional reason in C++11:

noexcept Destructors

by Andrzej Krzemieński

From the article:

The goal of this post is to show one — fairly small — backwards incompatibility in C++11. It shows how noexcept exception specifications are implicitly generated for your destructors. In short, the following program used to run successfully in C++03 (under some definition of “success”): ...

In this post I do not intend to argue whether it is a bad practice or not to throw from destructors, but focus on what happens when you do. But I really do not encourage you to throw from destructors...

GotW #7a Solution: Minimizing Compile-Time Dependencies, Part 1—Herb Sutter

By matt | Aug 19, 2013 07:05 AM | Tags: intermediate basics

The solution to the latest GotW problem is now available. In this Item, the focus is on analyzing and managing compile-time dependencies.

    GotW #7a Solution: Minimizing Compile-Time Dependencies, Part 1

    by Herb Sutter

From the article:

Managing dependencies well is an essential part of writing solid code. C++ supports two powerful methods of abstraction: object-oriented programming and generic programming. Both of these are fundamentally tools to help manage dependencies, and therefore manage complexity. It’s telling that all of the common OO/generic buzzwords—including encapsulation, polymorphism, and type independence—along with most design patterns, are really about describing ways to manage complexity within a software system by managing the code’s interdependencies.

When we talk about dependencies, we usually think of run-time dependencies like class interactions. In this Item, we will focus instead on how to analyze and manage compile-time dependencies. As a first step, try to identify (and root out) unnecessary headers.

Guideline: Never #include unnecessary header files.

Guideline: Prefer to #include <iosfwd> when a forward declaration of a stream will suffice.

Guideline: Never #include a header when a forward declaration will suffice.

Continue reading...

Resumable Functions: async and await -- Jens Weller

By Meeting C++ | Aug 18, 2013 10:21 AM | Tags: standardization performance experimental concurrency

JensWeller_small-da9313ea.jpgA look at resumable functions:

Resumable Functions: async and await

by Jens Weller

From the article:

While I did my series about the papers for Bristol, there was one paper, which I personally found a bit weird. This paper was about resumable functions, and at that time it was just another paper full of ideas for C++ to me. At C++Now suddenly, I got a better insight to what the use of resumable functions could be...

C++ String to Int -- Ivan Neeson

By Meeting C++ | Aug 16, 2013 08:53 AM | Tags: performance intermediate efficiency

kumobius.PNGA nice comparison on converting a string to int:

C++ String to Int

by Ivan Neeson

From the article:

In this post I will compare the following methods for parsing a string into an integer in C++:

  • Manually
  • atoi()
  • strtol()
  • sscanf()
  • std::stoi (C++11 only)
  • std::istringstream
  • Boost.LexicalCast
  • Boost.LexicalCast with C locale
  • Boost.Spirit.Qi
  • Boost.Coerce

But first lets look at the requirements...