CreateWindowEx, GetLastError, Windows 7, and XP oddities and odd behavior - winapi

Question

The following code works on Window 7, but when I run it on Windows XP, it fails with an error message returned by windows: "The system can not find the file specified".
#include <windows.h>
#include <windowsx.h>
#include <commctrl.h>
#include <uxtheme.h>
#include <string>
const char g_szClassName[] = "myWindowClass";
const char title[] = "Window Title\0";
COLORREF WinColor;
HFONT defaultFont;
NONCLIENTMETRICSA Metrics;
DWORD dwVersion;
DWORD dwMajorVersion;
DWORD dwMinorVersion;
HBRUSH hBrushColor;
bool LastError = false;
bool W32Error (const char * Msgtext);
// Step 4: the Window Procedure
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
case WM_NCCREATE:
{
Metrics.cbSize = sizeof(NONCLIENTMETRICS);
SystemParametersInfo (SPI_GETNONCLIENTMETRICS, sizeof(NONCLIENTMETRICS), &Metrics, 0);
defaultFont = (HFONT) CreateFontIndirect (& Metrics.lfMessageFont);
return TRUE;
}
break;
case WM_CTLCOLORSTATIC: {
dwVersion = GetVersion();
dwMajorVersion = (DWORD)(LOBYTE(LOWORD(dwVersion)));
dwMinorVersion = (DWORD)(HIBYTE(LOWORD(dwVersion)));
if ( (IsAppThemed()) && (dwMajorVersion < 6) ) {
WinColor = GetSysColor(COLOR_WINDOW);
SetBkColor((HDC)wParam, WinColor);
return (LRESULT)hBrushColor;
}
}
break;
case WM_CREATE: {
HWND hButton = CreateWindowEx(
0,
"BUTTON", "Button",
WS_TABSTOP |
WS_VISIBLE |
WS_CHILD |
BS_NOTIFY |
BS_PUSHBUTTON,
10, 10, 96, 32, hwnd,
(HMENU)50,
GetModuleHandle(NULL),
NULL);
if (W32Error ("Button Creation Failed\nReason:")) exit (1);
return TRUE;
}
break;
case WM_CLOSE:
DestroyWindow(hwnd);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPSTR lpCmdLine, int nCmdShow)
{
WNDCLASSEX wc;
HWND hwnd;
MSG Msg;
// Initialize common controls.
INITCOMMONCONTROLSEX icc;
icc.dwSize = sizeof(icc);
icc.dwICC = ICC_WIN95_CLASSES |
ICC_COOL_CLASSES |
ICC_INTERNET_CLASSES|
ICC_LINK_CLASS |
ICC_STANDARD_CLASSES|
ICC_PROGRESS_CLASS |
ICC_USEREX_CLASSES;
InitCommonControlsEx(&icc);
//Step 1: Registering the Window Class
wc.cbSize = sizeof(WNDCLASSEX);
wc.style = CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc = WndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wc.lpszMenuName = NULL;
wc.lpszClassName = g_szClassName;
wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
// see if something is going on before the window registration takes place....
if (W32Error ("Previous Check for Error?\nReason:")) exit (1);
if(!RegisterClassEx(&wc))
{
MessageBox(NULL, "Window Registration Failed!", "Error!",
MB_ICONEXCLAMATION | MB_OK);
return 0;
}
if (W32Error ("Window Registration Failed\nReason:")) exit (1);
// Step 2: Creating the Window
hwnd = CreateWindowEx(
WS_EX_CLIENTEDGE,
g_szClassName,
"The title of my window",
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT, 240, 120,
NULL, NULL, hInstance, NULL);
if (W32Error ("Window Creation Failed\nReason:")) exit (1);
if(hwnd == NULL)
{
MessageBox(NULL, "Window Creation Failed!", "Error!",
MB_ICONEXCLAMATION | MB_OK);
return 0;
}
SendMessageA(hwnd, WM_SETFONT, WPARAM (defaultFont), TRUE);
SendMessageA(hwnd, WM_SETTEXT, WPARAM(NULL) , LPARAM (title));
ShowWindow(hwnd, nCmdShow);
UpdateWindow(hwnd);
// Step 3: The Message Loop
while(GetMessage(&Msg, NULL, 0, 0) > 0)
{
TranslateMessage(&Msg);
DispatchMessage(&Msg);
}
return Msg.wParam;
}
bool W32Error (const char * Msgtext)
{
LPTSTR errorText = NULL;
DWORD dwLastError = GetLastError();
if (!dwLastError) {
LastError = false;
return LastError;
}
// use system message tables to retrieve error text
// allocate buffer on local heap for error text
// Important! will fail otherwise, since we're not (and CANNOT) pass insertion parameters
FormatMessageA(
FORMAT_MESSAGE_FROM_SYSTEM |
FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_IGNORE_INSERTS,
NULL, // unused with FORMAT_MESSAGE_FROM_SYSTEM
dwLastError,
MAKELANGID (LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPTSTR)&errorText, // output
0, // minimum size for output buffer
0); // arguments - see note
if ( NULL != errorText ) {
std::string Message;
Message += Msgtext;
Message += "\n";
Message += errorText;
MessageBoxA(NULL, (LPCSTR)Message.c_str(), "An Internal Error Occurred", MB_OK);
LocalFree(errorText);
errorText = NULL;
LastError = true;
} else {
LastError = false;
}
return LastError;
}
As an additional, I have a resource.rc and resource.h file linked in with winres that complies in a manifest.xml that provides a controls version 6 specification.
Ok, so here is the deal, This runs on Windows 7 without a hitch. And it runs on XP, unless I put in the line if (W32Error ("Window Registration Failed\nReason:")) exit (1);
(basically, it calls my error checking routine which includes GetLastError())
if(!RegisterClassEx(&wc))
{
MessageBox(NULL, "Window Registration Failed!", "Error!",
MB_ICONEXCLAMATION | MB_OK);
return 0;
}
if (W32Error ("Window Registration Failed\nReason:")) exit (1);
When I include that line, I get an error "The system can not find the file specified." The return value back from RegisterClassEx does not go into the if block, so RegisterClassEx returns Ok.
This only happens on Windows XP, it works just fine on Windows 7. If I don't include this line, it works as if nothing is wrong.
The point of this sample is to get themes to work right on both XP and Windows 7. (not an easy task.)
Why is RegisterClassEx returning Ok, but generates an error for GetLastError on Windows XP and not on Windows 7?
Also, what file is it looking for anyway? I have seen other Google results say It has to do with a messed up message loop or window procedure, but that's not the case here.

Answer 1

General mistake... Due to MSDN you may check GetLastError only when RegisterClassEx "return value is zero". When RegisterClassEx or CreateWindowEx or any other functions are succeeded, GetLastError may return garbage, there is no guarantee that GetLastError will returns zero (if different behavior does not described in Return value section).