VideoCapture::VideoCapture(const String& filename, int apiPreference) : throwOnFail(false)
{
    open(filename, apiPreference); // 1-1
}

VideoCapture::VideoCapture(int index, int apiPreference) : throwOnFail(false)
{
    open(index, apiPreference); // 2-1
}

bool VideoCapture::open(const String& filename, int apiPreference) // 1-1
{
    if (isOpened()) release();

    const std::vector<VideoBackendInfo> backends =
        cv::videoio_registry::getAvailableBackends_CaptureByFilename(); // 1-2

    for (size_t i = 0; i < backends.size(); i++)
    {
        const VideoBackendInfo& info = backends[i];
        if (apiPreference == CAP_ANY || apiPreference == info.id)
        {
            const Ptr<IBackend> backend = info.backendFactory->getBackend(); // 1-9 backendFactory
            if (!backend.empty())
            {
                try
                {
                    icap = backend->createCapture(filename); // 1-10
                    if (!icap.empty())
                    {
                        if (icap->isOpened())
                            return true;
                        icap.release();
                    }
                } catch(...) {
                    // ...
                }
            }
        }
    }

    return false;
}

bool  VideoCapture::open(int cameraNum, int apiPreference) // 2-1
{
    if (isOpened()) release();

    if (apiPreference == CAP_ANY)
    {
        // interpret preferred interface (0 = autodetect)
        int backendID = (cameraNum / 100) * 100;
        if (backendID)
        {
            cameraNum %= 100;
            apiPreference = backendID;
        }
    }

    const std::vector<VideoBackendInfo> backends =
        cv::videoio_registry::getAvailableBackends_CaptureByIndex(); // 2-2
    for (size_t i = 0; i < backends.size(); i++)
    {
        const VideoBackendInfo& info = backends[i];
        if (apiPreference == CAP_ANY || apiPreference == info.id)
        {
            const Ptr<IBackend> backend = info.backendFactory->getBackend();
            if (!backend.empty())
            {
                try
                {
                    icap = backend->createCapture(cameraNum);
                    if (!icap.empty())
                    {
                        if (icap->isOpened())
                            return true;
                        icap.release();
                    }
                } catch(...) {
                    // ...
                }
            }
        }
    }

    return false;
}

#define DECLARE_DYNAMIC_BACKEND(cap, name, mode) \
{ \
    cap, (BackendMode)(mode), 1000, name, createPluginBackendFactory(cap, name) \
}

#define DECLARE_STATIC_BACKEND(cap, name, mode, createCaptureFile, createCaptureCamera, createWriter) \
{ \
    cap, (BackendMode)(mode), 1000, name, createBackendFactory(createCaptureFile, createCaptureCamera, createWriter) \
}

// 1-5
static const struct VideoBackendInfo builtin_backends[] = 
{
    // ...
    // Windows
#ifdef HAVE_DSHOW
    DECLARE_STATIC_BACKEND(CAP_DSHOW, "DSHOW", MODE_CAPTURE_BY_INDEX, 0, create_DShow_capture, 0),
#endif

    // Linux, some Unix
#if defined HAVE_CAMV4L2 // 1-6
    DECLARE_STATIC_BACKEND(CAP_V4L2, "V4L2", MODE_CAPTURE_ALL, create_V4L_capture_file, create_V4L_capture_cam, 0),
#elif defined HAVE_VIDEOIO
    DECLARE_STATIC_BACKEND(CAP_V4L, "V4L_BSD", MODE_CAPTURE_ALL, create_V4L_capture_file, create_V4L_capture_cam, 0),
#endif
    // ...
};

class VideoBackendRegistry
{
protected:
    std::vector<VideoBackendInfo> enabledBackends;
    VideoBackendRegistry() // 1-4
    {
        const int N = sizeof(builtin_backends)/sizeof(builtin_backends[0]);
        enabledBackends.assign(builtin_backends, builtin_backends + N); // 1-5 builtin_backends
        for (int i = 0; i < N; i++)
        {
            VideoBackendInfo& info = enabledBackends[i];
            info.priority = 1000 - i * 10;
        }

        // ...
        std::sort(enabledBackends.begin(), enabledBackends.end(), sortByPriority); // 排序
    }

    // ...
    static VideoBackendRegistry& getInstance() // 1-3, 2-3 常見的 instance 技巧！
    {
        static VideoBackendRegistry g_instance; // 1-4 VideoBackendRegistry()
        return g_instance;
    }
    // ...
    inline std::vector<VideoBackendInfo> getAvailableBackends_CaptureByIndex() const // 2-4
    {
        std::vector<VideoBackendInfo> result;
        for (size_t i = 0; i < enabledBackends.size(); i++)
        {
            const VideoBackendInfo& info = enabledBackends[i];
            if (info.mode & MODE_CAPTURE_BY_INDEX)
                result.push_back(info);
        }
        return result;
    }
    inline std::vector<VideoBackendInfo> getAvailableBackends_CaptureByFilename() const // 1-8
    {
        std::vector<VideoBackendInfo> result;
        for (size_t i = 0; i < enabledBackends.size(); i++)
        {
            const VideoBackendInfo& info = enabledBackends[i];
            if (info.mode & MODE_CAPTURE_BY_FILENAME)
                result.push_back(info);
        }
        return result;
    }

};

namespace videoio_registry {

std::vector<VideoBackendInfo> getAvailableBackends_CaptureByIndex() // 2-2
{
    // 2-3 getInstance, 2-4 getAvailableBackends_CaptureByIndex
    const std::vector<VideoBackendInfo> result = VideoBackendRegistry::getInstance().getAvailableBackends_CaptureByIndex();
    return result;
}
std::vector<VideoBackendInfo> getAvailableBackends_CaptureByFilename() // 1-2
{
    // 1-3 getInstance, 1-8 getAvailableBackends_CaptureByFilename
    const std::vector<VideoBackendInfo> result = VideoBackendRegistry::getInstance().getAvailableBackends_CaptureByFilename();
    return result;
}
}

struct VideoBackendInfo {
    VideoCaptureAPIs id;
    BackendMode mode;
    int priority;     // 1000-<index*10> - default builtin priority
                      // 0 - disabled (OPENCV_VIDEOIO_PRIORITY_<name> = 0)
                      // >10000 - prioritized list (OPENCV_VIDEOIO_PRIORITY_LIST)
    const char* name;
    Ptr<IBackendFactory> backendFactory; // 1-9
};

class IBackend
{
public:
    virtual ~IBackend() {}
    virtual Ptr<IVideoCapture> createCapture(int camera) const = 0;
    virtual Ptr<IVideoCapture> createCapture(const std::string &filename) const = 0; // 1-10
    virtual Ptr<IVideoWriter>  createWriter(const std::string &filename, int fourcc, double fps, const cv::Size &sz, bool isColor) const = 0;
};

class IBackendFactory
{
public:
    virtual ~IBackendFactory() {}
    virtual Ptr<IBackend> getBackend() const = 0; // 要看是實作哪種 IBackendFactory
};

Ptr<IVideoCapture> create_DShow_capture(int index);
// ...
Ptr<IVideoCapture> create_V4L_capture_cam(int index); // 1-6, 1-7
// ...
Ptr<IVideoCapture> create_Images_capture(const std::string &filename);

Ptr<IVideoCapture> create_V4L_capture_cam(int index) // 1-7
{
    cv::CvCaptureCAM_V4L* capture = new cv::CvCaptureCAM_V4L(); // 下一篇再介紹

    if (capture->open(index))
        return makePtr<LegacyCapture>(capture);

    delete capture;
    return NULL;
}

#include <opencv2/opencv.hpp>

int main(void) {
    std::cout << cv::getBuildInformation() << std::endl;
}

#ifndef OPENCV_CVCONFIG_H_INCLUDED
#define OPENCV_CVCONFIG_H_INCLUDED

/* OpenCV compiled as static or dynamic libs */
#define BUILD_SHARED_LIBS

/* OpenCV intrinsics optimized code */
#define CV_ENABLE_INTRINSICS

/* OpenCV additional optimized code */
/* #undef CV_DISABLE_OPTIMIZATION */

/* Compile for 'real' NVIDIA GPU architectures */
#define CUDA_ARCH_BIN ""

/* Create PTX or BIN for 1.0 compute capability */
/* #undef CUDA_ARCH_BIN_OR_PTX_10 */

/* NVIDIA GPU features are used */
#define CUDA_ARCH_FEATURES ""

/* Compile for 'virtual' NVIDIA PTX architectures */
#define CUDA_ARCH_PTX ""

/* AVFoundation video libraries */
/* #undef HAVE_AVFOUNDATION */

/* V4L capturing support */
/* #undef HAVE_CAMV4L */

/* V4L2 capturing support */
#define HAVE_CAMV4L2

//...

#endif // OPENCV_CVCONFIG_H_INCLUDED

void UseRawPointer() {
    // 使用原始指標
    Song* pSong = new Song("Just The Way You Are", "Bruno Mars");

    // Use pSong...
    pSong->DoSomething();

    // 別忘了要 delete!
    delete pSong;
}

void UseSmartPointer() {
    // 使用智慧型指標
    shared_ptr<Song> song2(new Song("Just The Way You Are", "Bruno Mars"));

    // Use song2...
    song2->DoSomething();

} // song2 在這裡自動地被 deleted

// 盡可能地使用 make_shared
auto sp1 = make_shared<Song>("The Beatles", "Hey Jude");
// 或者不使用 auto 像這樣寫
shared_ptr<Song> sp1 = make_shared<Song>("The Beatles", "Hey Jude");

// 下面這樣的寫法也可以，但會有一些副作用，記憶體配置上不連續，以及分開記憶體配置效能相對低弱
// Note: Using new expression as constructor argument
// creates no named variable for other code to access.
shared_ptr<Song> sp2(new Song("Lady Gaga", "Poker Face"));

// When initialization must be separate from declaration, e.g. class members,
// initialize with nullptr to make your programming intent explicit.
shared_ptr<Song> sp5(nullptr);
//等於: shared_ptr<Song> sp5;
sp5 = make_shared<Song>("Avril Lavigne", "What The Hell");

void SmartPointerDemo2() {
    // Create the object and pass it to a smart pointer
    std::shared_ptr<LargeObject> pLarge(new LargeObject());

    // Call a method on the object
    pLarge->DoSomething();

    // 在離開函式前手動釋放記憶體
    pLarge.reset();

    // ...

}

{
    Object *p = new Object();
    std::shared_ptr<Object> sp(p);
    // ...
    std::shared_ptr<Object> sp2(p);
} // sp 釋放，表示 delete 該物件，再換 sp2 釋放，造成釋放重複記憶體

{
    std::shared_ptr<Object> sp(new Object());
} // sp 釋放

// g++ std-shared-ptr.cpp -o a.out -std=c++11
#include <iostream>
#include <string>
#include <memory>

class LargeObject {
public:
    void DoSomething() {
        printf("DoSomething\n");
    }
};

void LegacyLargeObjectFunction(LargeObject *lo) {
    printf("LegacyLargeObjectFunction\n");
    lo->DoSomething();
}

int main() {
    printf("===1===\n");
    // Create the object and pass it to a smart pointer
    std::shared_ptr<LargeObject> pLarge(new LargeObject());

    printf("===2===\n");
    // Call a method on the object
    pLarge->DoSomething();

    printf("===3===\n");
    // 傳遞原始指標給 legacy API
    LegacyLargeObjectFunction(pLarge.get());

    printf("===4===\n");
    // 用原始指標去接
    LargeObject *p = pLarge.get();
    LegacyLargeObjectFunction(p);

    printf("===5===\n");
    return 0;
}

// g++ std-shared-ptr-exp1.cpp -o a.out -std=c++11
#include <iostream>
#include <string>
#include <memory>

class LargeObject {
public:
    LargeObject() {
        printf("LargeObject::LargeObject()\n");
    }

    ~LargeObject() {
        printf("LargeObject::~LargeObject()\n");
    }

    void DoSomething() {
        printf("DoSomething, x=%d\n", x);
    }

    int x = 10;
};

int main() {
    printf("===1===\n");
    LargeObject *p = new LargeObject();
    p->DoSomething();
    printf("%p\n", p);

    printf("===2===\n");
    std::shared_ptr<LargeObject> pLarge(p);
    pLarge->DoSomething();
    printf("%p\n", pLarge.get());
    printf("%p\n", p);

    printf("===3===\n");

    //delete p; // double free or corruption

    printf("===4===\n");
    return 0;
}

auto song1 = new Song("Village People", "YMCA");
auto song2 = new Song("Village People", "YMCA");
shared_ptr<Song> p1(song1);
shared_ptr<Song> p2(song2);
shared_ptr<Song> p3(p2);
cout << "p1 == p2 = " << std::boolalpha << (p1 == p2) << endl;
cout << "p3 == p2 = " << std::boolalpha << (p3 == p2) << endl;

// g++ std-atomic_flag.cpp -o a.out -std=c++11 -pthread
#include <thread>
#include <vector>
#include <iostream>
#include <atomic>

std::atomic_flag lock = ATOMIC_FLAG_INIT;

void f(int n)
{
    for (int cnt = 0; cnt < 15; ++cnt) {
        while (lock.test_and_set(std::memory_order_acquire))  // acquire lock
             ; // spin 自旋
        std::cout << "Output from thread " << n << ", cnt = " << cnt << std::endl;
        lock.clear(std::memory_order_release);               // release lock
    }
}

int main()
{
    std::vector<std::thread> v;
    for (int n = 0; n < 3; ++n) {
        v.emplace_back(f, n);
    }
    for (auto& t : v) {
        t.join();
    }

    return 0;
}