Advanced C++ - Anonymous namespaces

Anonymous namespace is kind of namespace with no specified name. Such kind of namespace is visible only within file where it is defined within. I allows define variables and functions which could be visible as global, but within one file only. Thanks to that such files are not global within whole program. It also allow avoids making global static variable. Let's see an example of defining and usage of anonymous namespace. Consider following main.cpp file:
In the above example we have anonymous namespace containing one int typed variable. This variable can be used as global variable withing this main.cpp file but will not be visible inside any other files. That is simple example of usage anonymous variables. If you would like to compile it and play with it (changing or adding some parts of code to check what happends than) you can download it from here: https://github.com/xmementoit/CppAdventureExamples/tree/master/advancedCpp/anonymousNamespace

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STL - count and count_if algorithms

One of the basic and most useful STL algorithms is algorithm which can be used to count number of elements within selected container according to specified criteria. In order to do that we can use std::count or std::count_if algorithm. std::count (firstElementIterator, lastElementIterator, elementForSearch) - is function which will go through container using firstElementIterator and lastElementIterator and return number of container elements which value is equal elementForSearch std::count_if (firstElementIterator, lastElementIterator, UnaryPredicateFunction) - is function which examine range from firstElementIterator to lastElementIterator and return number of container elements which fulfill UnaryPredicateFunction criteria. UnaryPredicateFunction is function having following signature: bool functionName(const Type& a) . So, count_if returns number of elements where UnaryPredicateFunction returns true for. For better understanding let's take a...

QT - foreach algoriithm with const references performance improvement

Today I would like to show you optimal way of using foreach QT algorithm . I will show you why we should pass elements of foreach algorithm by const reference instead of passing them by value. Let me explain it on the below example: Output of this example is: In point I we are creating 3 objects of MyClass class and push them to myClasses QList element. In point II we are using QT foreach algorithm to invoke getValue() method for each object from myClasses list. As you can see on output text for that part of code we are invoking copy constructor before and destructor after invoking getValue() function. It is because we are passing each myClasses list element to foreach algorithm by value. Therefore we are copying that element at the beginning of foreach loop step and removing them (destructing) at the end. This is inefficient solution, especially when class of object being copied is big. It decreases performance. of our application. Solution for that i...

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