GotW #1: Variable Initialization—or Is It? -- Herb Sutter

By Blog Staff | May 6, 2013 06:46 PM | Tags: intermediate basics

Herb Sutter is resuming his Guru of the Week series of problem-and-solution articles about coding in C++, with the intent to gradually update the 88 existing issues and write a few more along the way.

The first problem was posted today:

GotW #1: Variable Initialization -- or Is It? (3/10)

by Herb Sutter

This first problem highlights the importance of understanding what you write. Here we have a few simple lines of code — most of which mean something different from all the others, even though the syntax varies only slightly.

The solution is coming "soon"...

Ownership and 'Memory -- Andy Balaam

By Blog Staff | May 3, 2013 04:41 PM | Tags: basics

A short and basic summary of C++'s view of memory management: You can worry about it a lot less, and still be efficient, if you say who owns what.

Goodness in programming languages, part 4 -- Ownership & Memory

by Andy Balaam

From the post:

... over time the community of C++ programmers has been developing a new way of thinking about memory, and developing tools in the C++ language to make it easier to work in this way.

Modern C++ code rarely or never uses “delete” or “free” to deallocate memory, but instead defines clearly which object owns each other object. ...

Quick Q: How do I use std::tie and std::ignore? -- StackOverflow

By Blog Staff | May 2, 2013 01:13 PM | Tags: basics

How well do you know tie and ignore, especially to use the C++11 multiple return value idiom?

Please explain this code that uses std::ignore

I'm reading the documentation on std::ignore from cppreference. I find it quite hard to grasp the true purpose of this object, and the example code doesn't do it much justice. For example, in the below code, how and why is inserted set to true? It doesn't make much sense to me.

#include <iostream>
#include <string>
#include <set>
#include <tuple>

int main()
{
    std::set<std::string> set_of_str;
    bool inserted;
    std::tie(std::ignore, inserted) = set_of_str.insert("Test");
    if (inserted) {
        std::cout << "Value was inserted sucessfully\n";
    }
}

If someone can explain the code to me, it would be appreciated. Thanks.

Quick Q: Why does shared_ptr of void work? -- StackOverflow

By Blog Staff | May 2, 2013 11:16 AM | Tags: intermediate basics

Quick A: When it comes to destruction, only your deleter knows for sure... but he's captured at construction time, so all starts well and stays well.

Why do std::shared_ptr<void> work

I found some code using std::shared_ptr to perform arbitrary cleanup at shutdown. At first I thought this code could not possibly work, but then I tried the following:

[edited]

int main() {
  vector<shared_ptr<void>> v;
  {
    v.push_back( shared_ptr<test>( new test() ) );
  }
} // [[ how can this destroy type-safely? ]]

Quick Q: Does [=] capture all variables in scope? -- StackOverflow

By Blog Staff | May 2, 2013 04:45 AM | Tags: basics

Quick A: No.

A simple but important question:

C++11 lambda capture semantics

When I use [=] to indicate that I would like all local variables to be captured by value in a lambda, will that result in all local variables in the function being copied, or just all local variables that are used by the lambda?

So, for example, if I have:

vector<int> my_huge_vector(100000);
int my_measly_int;
some_function([=](int i){ return my_measly_int + i; });

Will my_huge_vector be copied, even though I don't use it in the lambda?

Quick Q: static constexpr variable vs. constexpr function? -- StackOverflow

By Blog Staff | May 1, 2013 04:39 PM | Tags: intermediate basics

With a nice Quick A by Morwenn that not only gives the right answer as of today, but is current with a feature voted into C++14 just two weeks ago that lets you drop the ()'s:

static constexpr variable vs. function

Is there a difference between declaring floating point constant as a static constexpr variable and a function as in example below, or is it just a matter of style?

class MY_PI
{
public:
    static constexpr float MY_PI_VAR = 3.14f;
    static constexpr float MY_PI_FUN() { return 3.14f; }
}

An Idiot's Guide to C++ Templates -- Ajay Vijayvargiya

By Blog Staff | Apr 30, 2013 06:18 AM | Tags: intermediate

A lot of people appreciated the information in this pair of articles, which cover the noted topics:

An Idiot's Guide to C++ Templates -- Part 1

The Syntax Drama

Function Templates

• Pointers, References and Arrays with Templates
• Multiple Types with Function Templates
• Function Template -- Template Function
• Explicit Template Argument Specification
• Default Arguments with Function Templates

Class Templates

• Multiple Types with Class Templates
• Non-type Template Arguments
• Template Class as Argument to Class Template
• Default Template Arguments with Class Templates
• Class' Methods as Function Templates

An Idiot's Guide to C++ Templates -- Part 2

Requirements from the Underlying Type

• Requirements: Function Templates
• Requirements: Class Templates

Separation of Declaration and Implementation

• Separating Class Implementation

Templates and Other Aspects of C++

• Class Templates, Friends
• Class Templates, Operator Overloading
• Class Templates, Inheritance
• Function Pointers and Callbacks
• Templates and Virtual Functions
• Templates and Macros
• Function Overloading

STL - An Introduction

Templates and Library Development

Explicit Instantiation

C++ on the Web: Run Your Big 3D Game in the Browser! -- Andre Weissflog

By Blog Staff | Apr 26, 2013 02:37 PM | Tags: intermediate

Building C++ to target Javascript (e.g., asm.js) and execute C++ in the browser is becoming quite the popular indoor sport. Here's a current presentation and experience report:

C++ on the Web: Run your big 3D Game in the browser! (slides)

by Andre Weissflog
Head of Development, Berlin
Bigpoint GmbH

My presentation about porting large C/C++ code bases to the browser (emscripten, flascc, Google Native Client)

From the Wrap-up slide:

• You can run big C/C++ code bases ("a million lines of code") in the browser.
• Javascript is already fast enough for many types of games.
• Massive performance improvements happening right now (better code generation, JS engines better at running generated code, asm.js...)
• ...

Quick Q: When should I use noexcept? -- StackOverflow

By Blog Staff | Apr 24, 2013 03:25 AM | Tags: basics

As C++11-compliant compilers start to roll out and be adopted, people want to know to best use new C++11 features, such as:

When Should I Really Use noexcept?

 

1. There are many examples of functions that I know will never throw, but for which the compiler cannot determine so on its own. Should I append noexcept to the function declaration in all such cases? ... For which situations should I be more careful about the use of noexcept, and for which situations can I get away with the implied noexcept(false)?
2. When can I realistically except to observe a performance improvement after using noexcept? ... Do modern compilers take advantage of noexcept in this way? If not, can I excect some of them to do so in the near future?

Preconditions, Part 4 -- Andrzej Krzemieński

By Blog Staff | Apr 23, 2013 04:38 AM | Tags: intermediate

Here is Andrzej's final (for now) post on preconditions, posted just 

Preconditions — Part IV

by Andrzej Krzemieński

This is the last post about preconditions. We will try to address concerns about a potential UB connected with expressing preconditions. We will also try to explore how language support for preconditions could look like.

 

...

Such a support for preconditions would be a very helpful feature. But let’s not fantasize too much. For now the best thing we can do is to use assertions and comments -- a very useful and often underestimated language feature.