windows C2440 无法在 C++ WinApi 中将 LRESULT 转换为 WNDPROC
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C2440 Can't convert LRESULT to WNDPROC in C++ WinApi
提问by Ozzah
I'm trying to write this win32 program with WinApi and I'm stuck because the tutorial I'm following seems to have a problem.
我正在尝试用 WinApi 编写这个 win32 程序，但我被卡住了，因为我遵循的教程似乎有问题。
MainWindow.h:
主窗口.h：
class MainWindow
{
public:
MainWindow(HINSTANCE);
~MainWindow(void);
LRESULT CALLBACK WndProcedure(HWND, UINT, WPARAM, LPARAM);
// [...]
MainWindow.cpp:
主窗口.cpp：
MainWindow::MainWindow(HINSTANCE hInstance) : hwnd(0)
{
WNDCLASSEX WndClsEx;
// [...]
WndClsEx.lpfnWndProc = &MainWindow::WndProcedure;
// [...]
}
LRESULT CALLBACK MainWindow::WndProcedure(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
{
// [...]
}
I must be referencing MainWindow::WndProcedure wrong because I'm following the signature exactly as the tutorial says, however the lpfnWndProc line in the constructor gives a compile-time error:
我一定是引用了 MainWindow::WndProcedure 错误，因为我完全按照教程所说的那样遵循签名，但是构造函数中的 lpfnWndProc 行给出了编译时错误：
error C2440: '=' : cannot convert from 'LRESULT (__stdcall MainWindow::* )(HWND,UINT,WPARAM,LPARAM)' to 'WNDPROC'
错误 C2440：“=”：无法从“LRESULT (__stdcall MainWindow::*)(HWND,UINT,WPARAM,LPARAM)”转换为“WNDPROC”
回答by
replace
代替
LRESULT CALLBACK WndProcedure(HWND, UINT, WPARAM, LPARAM);
by
经过
static LRESULT CALLBACK WndProcedure(HWND, UINT, WPARAM, LPARAM);
The this pointer is a hidden parameter in your function call and by declaring it static the this pointer is not a parameter anymore and the signature of the two functions match.
this 指针是函数调用中的隐藏参数，通过将其声明为静态 this 指针不再是参数，并且两个函数的签名匹配。
回答by interjay
You can't use a non-static member function as a window procedure. If you declare WndProcedureas staticit should compile. A non-member function would work as well.
您不能将非静态成员函数用作窗口过程。如果你声明WndProcedure作为static它应该编译。非成员函数也可以工作。
Non-static member functions have a different signature than static members. This is because they receive an implicit thisparameter in addition to the explicitly defined parameters.
非静态成员函数与静态成员具有不同的签名。这是因为this除了显式定义的参数之外，它们还接收一个隐式参数。
回答by rodrigo
That's because your WndProcedure function must be either a global function or a staticmember function.
那是因为您的 WndProcedure 函数必须是全局函数或静态成员函数。
