November 2018

November 25, 2018February 11, 2019

C++17: std::shared_mutex, interface_sizes, void_t, std::bool_constant, logical operation metafunctions

Class shared_mutex

On some platforms shared_mutex is more effecient then shared_timed_mutex.

In C++17 was added shared_mutex.

Example of usage:

class MyCounter
{
public:
    int get() {
        std::shared_lock lock_(mutex_);
        return counter_;
    }
    void increment() {
        std::unique_lock lock_(mutex_);
        counter_++;
    }
    void reset() {
        std::unique_lock lock_(mutex_);
        counter_ = 0;
    }
private:
    std::shared_mutex mutex_;
    int counter_{ 0 };
};


int main()
{   
    MyCounter counter;
    std::mutex cout_mutex;
 
    auto lambda = [&counter, &cout_mutex]() {
        std::lock_guard lock_(cout_mutex);
        for (auto i = 0; i < 3; i++) {
            counter.increment();
            std::cout << counter.get() << std::endl;
        }
    };
 
    std::thread thread1(lambda);
    std::thread thread2(lambda);
 
    thread1.join();
    thread2.join();
 
    return 0;
}

class MyCounter

{

public:

int get() {

std::shared_lock lock_(mutex_);

return counter_;

}

void increment() {

std::unique_lock lock_(mutex_);

counter_++;

}

void reset() {

std::unique_lock lock_(mutex_);

counter_ = 0;

}

private:

std::shared_mutex mutex_;

int counter_{ 0 };

};

int main()

{

MyCounter counter;

std::mutex cout_mutex;

auto lambda = [&counter, &cout_mutex]() {

std::lock_guard lock_(cout_mutex);

for (auto i = 0; i < 3; i++) {

counter.increment();

std::cout << counter.get() << std::endl;

}

};

std::thread thread1(lambda);

std::thread thread2(lambda);

thread1.join();

thread2.join();

return 0;

}

Continue reading “C++17: std::shared_mutex, interface_sizes, void_t, std::bool_constant, logical operation metafunctions”

November 18, 2018

C++17: Modifications to existing features (Part 2)

Construction for values of fixed enums

Before C++17, variable of fixed enumeration was initialized like this:

enum class E: unsigned char{};
 
E e{E(5)};

enum class E: unsigned char{};

E e{E(5)};

if we will try to initialize like this:

E e{ 5 };

E e{ 5 };

we will have error: cannot convert ‘int’ to ‘E’ in initialization.

In C++17 it’s allowed to build.

Continue reading “C++17: Modifications to existing features (Part 2)”

November 18, 2018November 18, 2018

C++17: Modifications to existing features (Part 1)

Single-argument static_assert

In C++17 static_assert message was changed to optional, and it’s possible create static_assert without message.

For example:

template<typename T>
class A {
    static_assert(std::is_default_constructible_v<T>);
};
 
class X {
public:
    X(int) {}
};
 
int main()
{   
   A<X> a; // ERROR: static_assert failed
   return 0;
}

template<typename T>

class A {

static_assert(std::is_default_constructible_v<T>);

};

class X {

public:

X(int) {}

};

int main()

{

A<X> a; // ERROR: static_assert failed

return 0;

}

Continue reading “C++17: Modifications to existing features (Part 1)”