Example of IDesktopWallpaper::AdvanceSlideshow

#include <stdexcept> // runtime_error
#include <memory> // unique_ptr

#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <initguid.h> // CLSID_DesktopWallpaper, IID_IDesktopWallpaper
#include <shlobj.h> // COM nonsense

/*
    This requires linking against ole32 (pass `-lole32` if using GCC)

    THIS WAS WRITTEN QUICK AND DIRTY!!

    I tried to keep this example simple, but also not abandon best practices.

    The error checks only tell you that things blew up. You shoud log the
    error code along with other useful information (std::source_location, etc)
    so can also find out _why_ it blew up.

    I'm using a struct and a unique_ptr to automate lifetime management &
    clean-up of the COM resources (RAII). If you were writing this as part
    of a public API / library, you'd probably want to provide a more safe and
    stable interface which would require a more well-designed COM abstraction.
*/

struct raii_com
{
    [[nodiscard]] explicit raii_com(
        const tagCOINIT tag = COINIT_APARTMENTTHREADED)
    {
        if (CoInitializeEx(NULL, tag) != S_OK) throw std::runtime_error(
            "A raii_com instance failed to initialize :(");
    }

    ~raii_com() noexcept
    { CoUninitialize(); }
};

/*
    This is a type alias for a unique_ptr that will hold our IDesktopWallpaper
    resource, and a pointer to a custom deleter function. When the unique_ptr
    is destroyed, it will pass the IDesktopWallpaper* to the deleter function
    which will handle clean-up. Not perfect, but better than a raw pointer.
*/
using raii_desktop_wallpaper =
    std::unique_ptr<IDesktopWallpaper, void(*)(IDesktopWallpaper*)>;

// The `raii_com` argument just helps guarantee that one exists
raii_desktop_wallpaper desktop_wallpaper_factory(const raii_com&)
{
    // Create an instance of the wallpaper thingy
    IDesktopWallpaper* our_new_resource;
    if (CoCreateInstance(
            CLSID_DesktopWallpaper,
            NULL,
            CLSCTX_LOCAL_SERVER,
            IID_IDesktopWallpaper,
            reinterpret_cast<void**>(&our_new_resource))
        != S_OK)
            throw std::runtime_error(
                "desktop_wallpaper_factory() failed :(");

    // Define the clean-up function (Lambda here, but could be normal func).
    const auto our_custom_deleter{
        [](IDesktopWallpaper* const p) noexcept
        {
            if (p != nullptr)
                p->Release();
        }
    };

    // Implicitly construct and return a `raii_desktop_wallpaper`
    return {our_new_resource, our_custom_deleter};
}

int main()
{
    const raii_com com;
    const auto wallpaper{ desktop_wallpaper_factory(com) };

    if (wallpaper->AdvanceSlideshow(NULL, DSD_FORWARD) != S_OK)
        throw std::runtime_error("AdvanceSlideshow failed :(");

    // No need to call wallpaper->Release() or CoUninitialize() because
    // clean-up is managed by the wrapper object lifetimes

    return 0;
}