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Overload 124 is now available

By Blog Staff | Dec 4, 2014 09:13 PM | Tags: intermediate basics

overload-124.PNGOverload 124 is now available. It contains the following C++-related articles, and more:

 

Overload 124

Designing Observers in C++11

The observer pattern is over two decades old. Alan Griffiths fits a venerable design pattern into a contemporary context.

Order Notation in Practice

What does complexity measurement mean? Roger Orr reminds us of the academic definition and looks at some real life situations... std::sort is faster than qsort which can come as a surprise to those who assume C is always faster than C++.

Common reasons of using namespaces in C++ projects -- CoderGears Team

By Marcin Hoppe | Dec 4, 2014 03:20 AM | Tags: basics

CoderGears team draws some conclusions on how namespaces are used in C++ projects:

Common reasons of using namespaces in C++ projects

by CodeGears Team

From the article:

Namespaces in C++ are most often used to avoid naming collisions. Although namespaces are used extensively in recent C++ code, most older code does not use this facility. After exploring the source code of many C++ projects, here are some common reasons of using the namespaces in these projects...

A gotcha with Boost.Optional --Andrzej KrzemieĊ„ski

By Razvan Pascalau | Dec 3, 2014 11:50 AM | Tags: boost basics

Have you used the Boost.Optional library? There is one thing you might need to keep an eye on as explained by Andrzej.

  A gotcha with Optional

  by Andrzej Krzemieński

From the article:

This post is about one gotcha in Boost.Optional library. When starting to use it, you might get the impression that when you try to put optional<T> where T is expected, you will get a compile-time error. In most of the cases it is exactly so, but sometimes you may get really surprised...

Quick Q: How do I add elements to a 2D vector of ints?--StackOverflow

By Jared Mulconry | Dec 2, 2014 03:56 AM | Tags: basics

Quick A: Index into the desired sub-vector and call push_back.

Recently on SO:

Inserting elements into 2D vector

So I'm creating a class that implements an adjacency list. Currently in my class definition I initialized two vectors:

vector<vector<int>> adjList;
vector<int> neighbors;

and I declared two functions that I plan to use to make it:

bool constructAdjList();
bool insertIntoAdjList(int, int);

It's getting difficult wrapping my head around 2D vectors. I understand that it is essentially a vector of vectors, but I'm confused about how to insert a new value into one of the "subvectors". For example, I am able to create an adjacency list in createAdjList that is empty with the following loop:

for (int i = 0; i < numOfValues; i++){
    neighbors.push_back(0);
    adjList.push_back(neighbors);
    neighbors.clear();
}

But how can I say, push_back the value 5 to the 4th vector in adjList, which would be represented in my insertIntoAdjList function as

insertIntoAdjList(4, 5);

I know I can access a specific value in a 2D vector by saying adjList[4][1], but how can I push one onto it?

Thanks!

Quick Q: Does std::vector resize automatically when inserting new elements?--StackOverflow

By Jared Mulconry | Nov 28, 2014 09:54 AM | Tags: basics

Quick A: Yes.

Recently on SO:

Do Vectors resize automatically?

I am very sorry that I am asking such a beginner question but I am finding contradictory information online. I would ask at University but it is out until February next year.

Do Vectors resize automatically? Or do you need to check the current size periodically and resize when you need more room. It looks to be resizing for me automatically but I'm not sure if that is a feature or the compiler waving a magic wand.

Quick Q: What type do lambdas get compiled into? -- StackOverflow

By Blog Staff | Nov 14, 2014 09:37 AM | Tags: basics

Quick A: A compiler-generated type that stores the captured variables in its data members, and exposes the function signature and body as its operator().

Recently on SO:

What type do lambdas get compiled into?

As I know all data types must be known at compile time, and lambda is not a type. Does lambda got translated into anonymous struct with operator() or std::function wrapped?

For example,

std::for_each(v.begin(), v.end(), [](int n&){n++;});

Urbana Proposals - C++17 insight?

By Meeting C++ | Oct 25, 2014 01:59 AM | Tags: intermediate experimental c++17 c++ committee basics advanced

I've started with my series on the proposals for the next C++ Committee Meeting:

Urbana Proposals - C++17 insight?

by Jens Weller

From the article:

A short series to give you an overview over the Papers submitted in the latest mailing for the C++ Committee Meeting in Urbana-Champaign in Illinois. At the beginning of November the C++ Committee will have its 3rd Meeting this year. As C++14 is now finished, the focus is clearly on the upcoming C++17 standard.

Quick Q: Does unordered_map<string,MyClass>::erase() destroy my MyClass objects? -- SO

By Blog Staff | Oct 21, 2014 10:47 AM | Tags: basics

Quick A: No, but unordered_map<string, unique_ptr<MyClass>>::erase and unordered_map<string, shared_ptr<MyClass>>::erase do.

Today on SO:

std::unordered_map<std::String, myClass*> -- does std::unordered_map::erase() call myClass' DTor?

Assume I have some unordered_map of pointers to class instances, would erasing an object from that map also delete the instance?

(rewording the question:) If I wanted to delete that instance, which version would be right?

if(it != map.end())
{
    delete it->second;
    map.erase(it);
}

or simply

if(it != map.end())
    map.erase(it);

?