Author Archives: dmitriano

How we use forwarding references with ranges in C++

The parameter or print function is a forwarding reference because the range can change while being iterated, but the current value is l-value reference:

#include <string>
#include <vector>
#include <ranges>
#include <iostream>

template <class R, class Value>
concept range_over = std::ranges::range<R> &&
    std::same_as<std::ranges::range_value_t<R>, Value>;

template <range_over<std::string> Range>
void print(Range&& range)
{
    for (const std::string& val : range)
    {
        std::cout << val << std::endl;
    }
}
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Value category is a property of an expression in C++

The code below prints l-value:

#include <iostream>

namespace
{
    void foo(const int&)
    {
        std::cout << "const l-value" << std::endl;
    }

    void foo(int&)
    {
        std::cout << "l-value" << std::endl;
    }

    void foo(int&&)
    {
        std::cout << "r-value" << std::endl;
    }
}
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The right way to capture std::unique_ptr into a lambda expression

Starting from C++14:

#include <string>
#include <memory>

int main()
{
    std::unique_ptr<std::string> p = std::make_unique<std::string>("abc");

    auto func = [p = std::move(p)]()
    {
    };

    func();

    return 0;
}
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MSVC 2022 compiler bug

Static asserts in the code below do not fail with MSVC 19.32.31332 for x86:

#include <string>

int main()
{
    std::string v = "abc";

    auto func = [v]()
    {
        auto& l_ref = v;

        static_assert(std::is_same_v<decltype(l_ref), std::string&>);

        auto&& r_ref = std::move(v);

        static_assert(std::is_same_v<decltype(r_ref), std::string&&>);
    };

    func();

    return 0;
}

that is MSVC compiler bug. With GCC both l_ref and r_ref are const references.

Thanks to stackoverflow.com.

Reported this to Microsoft.

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Learning english with a data center technical support

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Switching to PHP 7.4 on Ubuntu 16.04

Some WordPress plugins stopped working with PHP 7.0 on my Ubuntu 16.04 server and I switched to PHP 7.4 with the following commands:

sudo add-apt-repository ppa:jczaplicki/xenial-php74-temp
sudo apt-get update
sudo apt-get install php7.4 php7.4-fpm php7.4-cli php7.4-mysql php7.4-dom php7.4-mbstring -y
service php7.4-fpm status
cd /etc/php/7.4/fpm/pool.d
sudo mv www.conf www.conf.dist
sudo mv ../../../7.0/fpm/pool.d/devnote.conf .
sudo service php7.0-fpm reload
sudo service php7.4-fpm reload
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An example of how r-value reference works in C++

An example of extending the lifetime of a temporary:

#include <iostream>

int main()
{
    int a = 1;
    int&& b = std::move(a);
    int&& c = b + 1;

    b = b + 1;
    c = c + 1;

    std::cout << a << b << c;
}

The output is:

223
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QObject::sender() is a slow function

I did not expect that its share of CPU usage in my app is 12.15%:

Why does it iterate over some collection? Isn’t there only one sender in a thread?

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Building QT 6.3.1 with OpenSSL for Windows

After various experimentation I was able to build QT 6.3.1 with OpenSSL for Windows with the following steps:

Extract archives with Bash:

tar -xzf ../distrib/openssl-1.1.1q.tar.gz
tar -xf ../distrib/qt-everywhere-src-6.3.1.tar.xz

Building OpenSSL 1.1.1q

Run the following commands with x64 Native Tools Command Prompt for VS 2022:

set PATH=%PATH%;C:\dev\PFiles\Strawberry\perl\bin
set PATH=%PATH%;C:\dev\PFiles\nasm-2.15.05
perl Configure VC-WIN64A
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Experimentation with OpenSSL and QT configuration on Windows

Building OpenSSL 1.1.1q with custom installation directory

Run the following commands with x64 Native Tools Command Prompt for VS 2022:

set PATH=%PATH%;C:\dev\PFiles\Strawberry\perl\bin
set PATH=%PATH%;C:\dev\PFiles\nasm-2.15.05
set MY_INSTALL_DIR=C:/dev/libs/OpenSSL
perl Configure VC-WIN64A --prefix="%MY_INSTALL_DIR%" --openssldir="%MY_INSTALL_DIR%"
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