Question

The following compiles without errors or warnings but doesn’t snag the IEFrame window, or at least I know it fails to change that window’s print orientation to landscape:

PRINTDLGEX pd;
pd.lStructSize = (DWORD)sizeof(PRINTDLG);    
BOOL GetPrinterDeviceDefaults(struct tagPDA* pd);

BOOL bRet=AfxGetApp()->GetPrinterDeviceDefaults(&pd); 
pd.hwndOwner = FindWindow("IEFrame", NULL);
LPDEVMODE pDevMode = (LPDEVMODE)::GlobalLock(&pd.hDevMode);
pDevMode->dmOrientation = DMORIENT_LANDSCAPE;
::GlobalUnlock(&pd.hDevMode);

I have evidence the code may have acquired the hWnd of the IEFrame window because the results of MessageBox(0,(LPCSTR)pd.hwndOwner,"[header]",MB_OK); displays some text gobbledygook in the msg. instead of nothing.

Thanks for any help.

Answer 1

I’m not at all familiar with the PRINTDLG API you’re trying to use, but your MessageBox code is all wrong.

The MessageBox function takes two pointers to null-terminated C strings (either ANSI strings or Unicode strings, depending on whether UNICODE is defined by the preprocessor). You’re passing in a window handle instead, which is not a null-terminated C string of any type — it’s just an opaque data value that only has meaning to the kernel. So when MessageBox tries to interpret the string, it gets a pointer to who-knows-where, and it will either crash with an access violation or read random gobbledygook out of memory until it runs into a stray NUL byte.

Ordinarily the compiler will give you an error here, but by inserting the cast you’re telling “it’s OK, I know what I’m doing, I promise this is really an LPCTSTR“, which masks the error.

The correct fix to this is to print the handle value into a character array. For example:

#define DIM(x) (sizeof(x)/sizeof((x)[0]))
wchar_t handleStr[64];
_snprintf_s(handleStr, DIM(handleStr), _TRUNCATE, "Handle value: %p", (void*)pd.hwndOwner);
MessageBoxW(NULL, handleStr, L"[header]", MB_OK);