郑君的学习笔记

using IntFloatString = std::variant<int, float, std::string>; // 定义支持int、float、string三个类型，并取一个别名
//初始化一个variant
TEST_F(InitVariant) {

    IntFloatString i = 10;
    ASSERT_EQ(10, std::get<int>(i) );

    IntFloatString f = 20.0f;
    ASSERT_EQ(20.0f, std::get<float>(f) );

    IntFloatString s = "hello world";
    ASSERT_EQ("hello world", std::get<std::string>(s));
}

unary right fold (pack op …)
unary left fold (… op pack)
binary right fold (pack op … op init)
binary left fold (init op … op pack)

template<typename... Args>
auto sub_val_right(Args&&... args) {
    return (args - ...);
}


template<typename... Args>
auto sub_val_left(Args&&... args) {
    return (... - args);
}

auto t = sub_val_right(2,3,4); //(2-(3-4)) = 3
auto t1 = sub_val_left(2,3,4); //((2-3)-4) = -5

template<typename... Args>
auto sub_one_left(Args&&... args) {
    return (1 - ... - args);
}

template<typename... Args>
auto sub_one_right(Args&&... args) {
    return (args - ... - 1);
}

auto t = sub_one_left（2，3，4);// (((1-2)-3)-4) = -8
auto t1 = sub_one_right（2，3，4);//(2-(3-(4-1))) = 2

// For 16 bit numbers:
unsigned short _byteswap_ushort(unsigned short value);
// For 32 bit numbers:
unsigned long _byteswap_ulong(unsigned long value);
// For 64 bit numbers:
unsigned __int64 _byteswap_uint64(unsigned __int64 value);

#include <climits>

template <typename T>
T swap_endian(T u)
{
    static_assert (CHAR_BIT == 8, "CHAR_BIT != 8");

    union
    {
        T u;
        unsigned char u8[sizeof(T)];
    } source, dest;

    source.u = u;

    for (size_t k = 0; k < sizeof(T); k++)
        dest.u8[k] = source.u8[sizeof(T) - k - 1];

    return dest.u;
}

swap_endian<uint32_t>(42);

#ifdef _MSC_VER

#include <stdlib.h>
#define bswap_32(x) _byteswap_ulong(x)
#define bswap_64(x) _byteswap_uint64(x)

#elif defined(__APPLE__)

// Mac OS X / Darwin features
#include <libkern/OSByteOrder.h>
#define bswap_32(x) OSSwapInt32(x)
#define bswap_64(x) OSSwapInt64(x)

#elif defined(__sun) || defined(sun)

#include <sys/byteorder.h>
#define bswap_32(x) BSWAP_32(x)
#define bswap_64(x) BSWAP_64(x)

#elif defined(__FreeBSD__)

#include <sys/endian.h>
#define bswap_32(x) bswap32(x)
#define bswap_64(x) bswap64(x)

#elif defined(__OpenBSD__)

#include <sys/types.h>
#define bswap_32(x) swap32(x)
#define bswap_64(x) swap64(x)

#elif defined(__NetBSD__)

#include <sys/types.h>
#include <machine/bswap.h>
#if defined(__BSWAP_RENAME) && !defined(__bswap_32)
#define bswap_32(x) bswap32(x)
#define bswap_64(x) bswap64(x)
#endif

#else

#include <byteswap.h>

#endif

#define WNDCLASS_NAME (L"CCanvas")

BOOL CCanvas::RegisterWndClass()
{
	WNDCLASS windowclass;
	HINSTANCE hInst = AfxGetInstanceHandle();

	//Check weather the class is registerd already
	if (!(::GetClassInfo(hInst, WNDCLASS_NAME, &windowclass)))
	{
		//If not then we have to register the new class
		windowclass.style = CS_DBLCLKS;// | CS_HREDRAW | CS_VREDRAW;
		windowclass.lpfnWndProc = ::DefWindowProc;
		windowclass.cbClsExtra = windowclass.cbWndExtra = 0;
		windowclass.hInstance = hInst;
		windowclass.hIcon = NULL;
		windowclass.hCursor = AfxGetApp()->LoadStandardCursor(IDC_ARROW);
		windowclass.hbrBackground = ::GetSysColorBrush(COLOR_WINDOW);
		windowclass.lpszMenuName = NULL;
		windowclass.lpszClassName = WNDCLASS_NAME;

		if (!AfxRegisterClass(&windowclass))
		{
			AfxThrowResourceException();
			return FALSE;
		}
	}

	return TRUE;
}

CCanvas::CCanvas()
{
	RegisterWndClass();
}

CCanvas m_canvas;//This is our custom control

void CdrawDemoDlg::DoDataExchange(CDataExchange* pDX)
{
	CDialogEx::DoDataExchange(pDX);
	DDX_Control(pDX, IDC_STATIC_FRAME, m_ctrl_draw);
	DDX_Control(pDX, IDOK, m_btn_ok);
	DDX_Control(pDX, IDC_CUSTOM1, m_canvas);
}

#define WNDCLASS_NAME (L"CCanvas")

BOOL CCanvas::RegisterWndClass()
{
	WNDCLASS windowclass;
	HINSTANCE hInst = AfxGetInstanceHandle();

	//Check weather the class is registerd already
	if (!(::GetClassInfo(hInst, WNDCLASS_NAME, &windowclass)))
	{
		//If not then we have to register the new class
		windowclass.style = CS_DBLCLKS;// | CS_HREDRAW | CS_VREDRAW;
		windowclass.lpfnWndProc = ::DefWindowProc;
		windowclass.cbClsExtra = windowclass.cbWndExtra = 0;
		windowclass.hInstance = hInst;
		windowclass.hIcon = NULL;
		windowclass.hCursor = AfxGetApp()->LoadStandardCursor(IDC_ARROW);
		windowclass.hbrBackground = ::GetSysColorBrush(COLOR_WINDOW);
		windowclass.lpszMenuName = NULL;
		windowclass.lpszClassName = WNDCLASS_NAME;

		if (!AfxRegisterClass(&windowclass))
		{
			AfxThrowResourceException();
			return FALSE;
		}
	}

	return TRUE;
}

CCanvas::CCanvas()
{
	RegisterWndClass();
}

CCanvas m_canvas;//This is our custom control

void CdrawDemoDlg::DoDataExchange(CDataExchange* pDX)
{
	CDialogEx::DoDataExchange(pDX);
	DDX_Control(pDX, IDC_STATIC_FRAME, m_ctrl_draw);
	DDX_Control(pDX, IDOK, m_btn_ok);
	DDX_Control(pDX, IDC_CUSTOM1, m_canvas);
}