为什么没有显示窗口？

[taozhuo]

以下程序执行后为什么没有窗口显示：
#include "windows.h"
LRESULT CALLBACK WndProc(HWND,UINT,WPARAM,LPARAM);

int WINAPI WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nShowCmd)
{
HWND hwnd;
MSG message;
WNDCLASS wndclass;
char lpszClassName[]="windows";
char lpszTitle[]="my_windows";
wndclass.style=0;
wndclass.lpfnWndProc=WndProc;
wndclass.cbClsExtra=0;
wndclass.cbWndExtra=0;
wndclass.hIcon=LoadIcon(NULL,IDI_APPLICATION);
wndclass.hCursor=LoadCursor(NULL,IDC_ARROW);
wndclass.hbrBackground=(HBRUSH)GetStockObject(WHITE_BRUSH);
wndclass.lpszMenuName=NULL;
wndclass.lpszClassName=lpszClassName;
if (!RegisterClass(&wndclass))
{
MessageBeep(0);
return FALSE;
}
hwnd=CreateWindow("hi","hi",WS_OVERLAPPEDWINDOW,CW_USEDEFAULT,CW_USEDEFAULT,
CW_USEDEFAULT,CW_USEDEFAULT,NULL,NULL,hInstance,NULL);
ShowWindow(hwnd,nShowCmd);
UpdateWindow(hwnd);

//message loop
while (GetMessage(&message,NULL,0,0))
{
TranslateMessage(&message);
DispatchMessage(&message);
}

return message.wParam;
}

//window procedure
LRESULT CALLBACK WndProc(HWND hwnd,UINT imessage,WPARAM wparam,LPARAM lparam)
{
switch(imessage)
{
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hwnd,imessage,wparam,lparam);
}
return(0);
}

[xiaoxiaohan]

wcex.cbSize = sizeof(WNDCLASSEX); //这个你没有

wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = (WNDPROC)WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(hInstance, (LPCTSTR)IDI_TEST);
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wcex.lpszMenuName = (LPCSTR)IDC_TEST;
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, (LPCTSTR)IDI_SMALL); //这个你没有