Category Archives: Programming languages

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16
06
22
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Switching to a different thread with async/await in C#

Posted by | C# |

The code below switches to a different thread when the execution of Main() is resumed at line 11:

internal class Program
{
    static async Task Main(string[] args)
    {
        try
        {
            HttpClient client = new HttpClient();

            Console.WriteLine($"Thread: {Thread.CurrentThread.ManagedThreadId}");
                
            HttpResponseMessage response = await client.GetAsync("https://developernote.com/");

            Console.WriteLine($"Thread: {Thread.CurrentThread.ManagedThreadId}");

            response.EnsureSuccessStatusCode();

            string responseBody = await response.Content.ReadAsStringAsync();

            Console.WriteLine($"Thread: {Thread.CurrentThread.ManagedThreadId}");

            Console.WriteLine(responseBody);
        }
        catch (HttpRequestException e)
        {
            Console.WriteLine("\nException Caught!");

            Console.WriteLine($"Thread: {Thread.CurrentThread.ManagedThreadId}");

            Console.WriteLine($"Message: {e.Message}");
        }
    }
}
(more…)
10
06
22
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My experimentation with QML Repeater

Posted by | QML, QT |

I was able to define a Repeater that displays cryptocurrency market orders:

(more…)
09
02
22
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Waitable QTimer with C++20 coroutines

Posted by | C++, QT |

Found an example of overriding co_await operator and was able to implement my own version:

#include <QTimer>
#include <QMetaObject>

#include <chrono>
#include <coroutine>

//QTimer accepts only milliseconds.
class TimeAwaitable
{
public:

    explicit TimeAwaitable(std::chrono::milliseconds d) : m_d(d) {}

    ~TimeAwaitable()
    {
        if (m_connection)
        {
            QObject::disconnect(m_connection);
        }
    }

    bool await_ready() const noexcept
    {
        return m_d <= std::chrono::milliseconds(0);
    }

    void await_suspend(std::coroutine_handle<> h) noexcept
    {
        m_connection = QObject::connect(&m_timer, &QTimer::timeout,
            [this, h]()
            {
                QObject::disconnect(m_connection);

                h.resume();
            });

        m_timer.setSingleShot(true);
        m_timer.start(m_d);
    }

    void await_resume() const noexcept {}

private:

    std::chrono::milliseconds m_d;
        
    QTimer m_timer;

    QMetaObject::Connection m_connection;
};

inline TimeAwaitable operator co_await(std::chrono::milliseconds d) noexcept
{
    return TimeAwaitable{ d };
}

For those who did not work with QT, QTimer::singleShot simply calls the lambda on the current thread after a given interval.

(more…)
18
01
22
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An example of real-time TableView in QML

Posted by | QML, QT |

Looks like CheckBox-es respond to clicks and work correctly even if they are in a TableView that is updated once a second:

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09
12
21
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Replace a substring in source file names

Posted by | Bash |

For example, the command below

find -name "*android*" -exec rename 's/android/windows/' {} \;

renames the following source files:

androidinappproduct.cpp
androidinappproduct.h
androidinapppurchasebackend.cpp
androidinapppurchasebackend.h
androidinapptransaction.cpp
androidinapptransaction.h
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29
09
21
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Using QML_ELEMENT with CMake

Posted by | QML, QT |

There is an example of using QML_ELEMENT in qt5\qtdeclarative\examples\quick\scenegraph\openglunderqml and qt_add_qml_module in CMake:

qt_add_qml_module(openglunderqml
    URI OpenGLUnderQML
    VERSION 1.0
    QML_FILES main.qml
    RESOURCE_PREFIX /scenegraph/openglunderqml
    NO_RESOURCE_TARGET_PATH
)

In QML it imports the module:

import OpenGLUnderQML 1.0
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10
09
21
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Adding a header to source files

Posted by | Bash |

Put the header content into a text file and load it into a variable:

cd ~/temp/
nano h.txt
h=$(<h.txt)
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07
09
21
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Did you already learn what are C++ concepts?

Posted by | C++ |

In C++20 we can do this:

#include <ranges>
#include <vector>

template <std::ranges::range Range>
    requires std::same_as<std::ranges::range_value_t<Range>, int>
auto TransformIt(Range r)
{
    return r | std::views::transform([](int n) { return n * n; });
}

int main()
{
    std::vector<int> v;
    auto r = TransformIt(v);
    return 0;
}
(more…)
05
09
21
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std::unique_ptr with a deleter that throws an exception

Posted by | C++ |

The program below is terminated when the deleter throws the exception:

#include <iostream>
#include <memory>

struct X
{
    int value;
};

struct Deleter
{
    void operator()(X* p) noexcept(false)
    {
        if (p->value == 0)
        {
            throw std::logic_error("Can't delete a zero.");
        }

        delete p;
    }
};
(more…)
28
08
21
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An example of heterogeneous lookup with std::unordered_set in C++20

Posted by | C++ |

std::unordered_set has a template find function in C++20. To make it work I define a custom hash and a custom equality compares as follows:

struct BotSettings
{
    std::string type;
    std::string name;
    bool started;
};
(more…)
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