Simple progress indicator for console proof of concept

ProgressIndicator.cpp

// Code written by cire, hereby released into the public domain.

#include <sstream>
#include <iomanip>
#include <iostream>
#include <thread>
#include <atomic>
#include <chrono>
#include <array>

class ProgressIndicator
{
public:
    typedef std::chrono::milliseconds duration_type;

    ProgressIndicator(duration_type delay = duration_type(500))
        : _percent(0), _delay(delay), _animationFrame(0) {}

    void update(unsigned percent) { _percent = percent ; }
    void display( std::ostream& os ) const;
    bool done() const { return _percent == 100; }

private:
    void _sleep() const { std::this_thread::sleep_for(_delay); }

    std::atomic<unsigned> _percent;
    const std::chrono::milliseconds _delay;

    mutable std::size_t _animationFrame;
    static std::array<char, 4> cursorAnimation ;
};

std::array<char, 4> ProgressIndicator::cursorAnimation = { '\\', '|', '/', '-' };

void fill(std::ostream& os, char ch, unsigned length, const char* str = "")
{
    os << std::setfill(ch) << std::setw(length) << str;
}

void ProgressIndicator::display(std::ostream& out) const
{
    const std::size_t indicatorLength(40);
    const std::size_t separatorLength(2);       
    const std::size_t digitalLength(3);         // 3 digits to accomodate 100.  
    const unsigned percent = _percent;

    std::ostringstream os;

    unsigned solidLen = static_cast<unsigned>(indicatorLength * (percent / 100.0));
    fill(os, '*', solidLen);

    if (solidLen < indicatorLength)
    {
        os << cursorAnimation[_animationFrame];
        fill(os, '.', indicatorLength - (solidLen + 1));
    }

    fill(os, ' ', separatorLength);
    os << std::setw(digitalLength) << std::to_string(percent) << '%';

    _animationFrame = (_animationFrame + 1) % cursorAnimation.size();

    fill(out, '\b', os.str().length());
    out << os.str() << std::flush;

    _sleep();
}

void spindicator(const ProgressIndicator* indicator)
{
    while (!indicator->done())
        indicator->display(std::cout);

    indicator->display(std::cout);
}

int main()
{
    ProgressIndicator indicator(std::chrono::milliseconds(200));
    std::thread indicatorThread(spindicator, &indicator);

    for (unsigned i = 0; i < 26; ++i)
    {
        std::this_thread::sleep_for(std::chrono::seconds(1));
        indicator.update(i * 4);
    }
    indicatorThread.join();
    std::cout << '\n';
}