Question

VS10：MCBS：你好，鉴于此discussion使用Pudeyev的How can I make a WNDPROC or DLGPROC a member of my C++ class?在code for "Hello World"尝试使用Hello World实现Raymond Chen的方法时遇到问题：

error LNK2001: unresolved external symbol "private: long __thiscall
BaseWnd::WndProc(struct HWND__ *,unsigned int,unsigned int,long)" 
(?WndProc@BaseWnd@@AAEJPAUHWND__@@IIJ@Z)

代码如下：

// ...Written by Oleg Pudeyev, (c) 2003
#include <windows.h>
HINSTANCE appHinst;

class BaseWnd
{
public:
BaseWnd();

// This is the static callback that we register
static LRESULT CALLBACK s_WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

// The static callback recovers the "this" pointer and then calls this member function.
LRESULT BaseWnd::WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

};

BaseWnd::BaseWnd(void)
{
    WNDCLASSW wc = {
        // Request redraws as we're centering the string
        CS_HREDRAW|CS_VREDRAW,
        BaseWnd::s_WndProc,
        // No per-class data
        0,
        // No per-window data
        0,
        appHinst,
        LoadIcon(0, IDI_APPLICATION),
        LoadCursor(0, IDC_ARROW),
        HBRUSH(COLOR_BACKGROUND),
        0,
        L"BaseWnd"
    };
RegisterClassW(&wc);
HWND hwnd = CreateWindowW(L"BaseWnd", L"Hello, World!", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, 0, 0, appHinst, this);
ShowWindow(hwnd, SW_SHOW);
}

LRESULT BaseWnd::WndProc(HWND hwnd, UINT Umsg, WPARAM wParam, LPARAM lParam)
{
switch (Umsg)
{
case WM_DESTROY:
PostQuitMessage(0);
break;

case WM_PAINT:
PAINTSTRUCT ps;
BeginPaint(hwnd, &ps);
RECT r;
GetClientRect(hwnd, &r);
SetBkMode(ps.hdc, TRANSPARENT);
DrawTextW(ps.hdc, L"Hello, World!", -1, &r, DT_CENTER|DT_VCENTER|DT_SINGLELINE);
EndPaint(hwnd, &ps);
break;

default:
// Use default handling for messages we don't process
return DefWindowProc(hwnd, Umsg, wParam, lParam);
}
return 0;
}

LRESULT CALLBACK BaseWnd::s_WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
BaseWnd *pThis; // our "this" pointer will go here

if (uMsg == WM_NCCREATE) {
// Recover the "this" pointer which was passed as a parameter to CreateWindow(Ex).
LPCREATESTRUCT lpcs = reinterpret_cast<LPCREATESTRUCT>(lParam);
pThis = static_cast<BaseWnd*>(lpcs->lpCreateParams);
// Put the value in a safe place for future use
SetWindowLongPtr(hwnd, GWLP_USERDATA, reinterpret_cast<LONG_PTR>(pThis));
} else {
// Recover the "this" pointer from where our WM_NCCREATE handler stashed it.
pThis = reinterpret_cast<BaseWnd*>(GetWindowLongPtr(hwnd, GWLP_USERDATA));
}

if (pThis) {
// Now that we have recovered our "this" pointer, let the member function finish the job.
//Removal of this line removes the LNK2001
return pThis->WndProc(hwnd, uMsg, wParam, lParam);
}

// "this" pointer unknown, so just do the default thing. Hopefully, didn't need to customize behavior yet.
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}


int WINAPI WinMain(HINSTANCE hinst, HINSTANCE hprev, LPTSTR cmdline, int showcmd)
{
appHinst = hinst;
BaseWnd p;
MSG msg;
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return 0;
}

调用BaseWnd构造函数的方式或类设置是否有问题 - 或者可能是Raymond的文章上的日期，c ++ 11的修订无法应对？

编辑：用绝对限定符BaseWnd :: WndProc替换WndProc，并使违规静态回调成为回调。很好，我们可以使用的代码的其他问题。
编辑2：拼图的最后一部分是将Pudeyev的原始CS_HREDRAW|CS_VREDRAW返回到WNDCLASS结构。

Answer 1

显然我认为范围的定义是没有的。

LRESULT CALLBACK WndProc
{
　↓
LRESULT CALLBACK BaseWnd::WndProc
{

Answer 2

错误应该是不言自明的。 BaseWnd::WndProc已声明，但未定义。见@nariuji

同样BaseWnd需要一个公共构造函数，因为您稍后会调用它：

class BaseWnd
{
//******* make this public:
public:
BaseWnd();
...
};

WNDCLASSW wc必须初始化为零：

WNDCLASSW wc = { 0 };

创建窗口时，它是不可见的。您必须使用ShowWindow将其显示或将样式更改为WS_VISIBLE | WS_OVERLAPPEDWINDOW

HWND hwnd = CreateWindowW(L"BaseWnd", L"Hello, World!", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, 0, 0, appHinst, this);
ShowWindow(hwnd, SW_SHOW); //*** add this

声明指针不做任何事情。您还需要一个消息循环：

WinMain(...)
{
    //BaseWnd *pthis; //***remove this line
    BaseWnd wnd;//***add this line
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    ...
}

LNK2001在“如何使WNDPROC或DLGPROC成为我的C ++类的成员？”

2 个答案: