winapi dialogbox doesn't show - visual-studio-2010

Question

I have the problem with my dialog, that when i invoke the function "DialogBoxA" the Dialog doesn't appear. I only get the "Busy Cursor" and the the cursor is also trapped inside of a small rectangle (the size of the dialog). After the press of (almost) any button it magically appears.
Dialog box call
DialogBoxA(hInstance,MAKEINTRESOURCEA(IDD_ORACLE_DIALOG),0,reinterpret_cast<DLGPROC>(DlgProc));
Dialog resource code
IDD_ORACLE_DIALOG DIALOGEX 0, 0, 155, 71
STYLE DS_SETFONT | DS_MODALFRAME | DS_FIXEDSYS | DS_CENTER | WS_POPUP | WS_VISIBLE | WS_CAPTION | WS_SYSMENU
CAPTION "Dialog"
FONT 8, "MS Shell Dlg", 400, 0, 0x1
BEGIN
DEFPUSHBUTTON "OK",IDOK,43,50,50,14
PUSHBUTTON "Cancel",IDCANCEL,98,50,50,14
COMBOBOX IDC_COMBOSERVER,53,6,94,30,CBS_DROPDOWN | CBS_SORT | CBS_NOINTEGRALHEIGHT | WS_VSCROLL | WS_TABSTOP
EDITTEXT IDC_EDITLOG,54,25,94,14,ES_AUTOHSCROLL
LTEXT "Server",IDC_STATIC,7,7,47,13
LTEXT "Log",IDC_STATIC,7,25,47,13
END
DialogProc
LRESULT CALLBACK DlgProc(HWND hWndDlg, UINT Msg, WPARAM wParam,LPARAM lParam){
switch(Msg){
case WM_INITDIALOG:
for(auto it = vServerList.begin();it!=vServerList.end();++it){
SendMessageA(GetDlgItem(hWndDlg,IDC_COMBOSERVER),CB_ADDSTRING,0,reinterpret_cast<LPARAM>(it->c_str()));
}
if(vServerList.size()>0){
SendMessage(GetDlgItem(hWndDlg,IDC_COMBOSERVER),CB_SETCURSEL,0,0);
SendMessage(GetDlgItem(hWndDlg,IDC_EDITLOG),WM_NCLBUTTONDOWN,HTCAPTION,0);
}else{
SendMessage(GetDlgItem(hWndDlg,IDC_COMBOSERVER),WM_NCLBUTTONDOWN,HTCAPTION,0);
}
#ifdef _DEBUG
SendMessageA(GetDlgItem(hWndDlg,IDC_EDITLOG),WM_SETTEXT,0,reinterpret_cast<LPARAM>("q40log"));
#endif
return TRUE;
case WM_COMMAND:
switch(wParam){
case IDOK:
size_t tServer,tLog;
tServer = GetWindowTextLength(GetDlgItem(hWndDlg,IDC_COMBOSERVER))+1;
tLog = GetWindowTextLength(GetDlgItem(hWndDlg,IDC_EDITLOG))+1;
char *pszServer,*pszLog;
pszServer = static_cast<char*>(calloc(tServer,sizeof(char)));
pszLog = static_cast<char*>(calloc(tLog,sizeof(char)));
GetDlgItemTextA(hWndDlg,IDC_COMBOSERVER,pszServer,tServer);
GetDlgItemTextA(hWndDlg,IDC_EDITLOG,pszLog,tLog);
szServer = pszServer;
szUser = pszLog;
free(pszServer);
free(pszLog);
EndDialog(hWndDlg,0);
return TRUE;
case IDCLOSE:
case IDCANCEL:
EndDialog(hWndDlg,0);
return FALSE;
}
break;
}
return FALSE;
}

Answer 1

The obvious failure modes are:
The dialog procedure is faulty.
The dialog resource is invalid.
The dialog resource is linked incorrectly and so cannot be loaded.
The instance handle is incorrect.
Of these options, the cast that you used in the dialog procedure parameter, it seems very likely that the dialog procedure is faulty.
I expect that you added the cast because the code would not compile. And it would not compile because the dialog procedure has an incorrect signature. The cast does not change that fact. It is just a way for you to suppress the compiler and tell it that you know better than it does. Generally speaking, the compiler tends to be right. If your dialog procedure has the wrong signature you need to correct it. Refer to the documentation to find out the correct signature.
The other big problem with your code is that you ignore the return value of DialogBox. If the function fails then the documentation tells you that a value of 0 or -1. In that scenario you can call GetLastError to get extended error information. You must get into the habit of checking for errors when using Win32 API functions.