Petzold's MessageBoxPrintf

[Sumit RAJAN]

In the second Chapter of Charles Petzold's "Programming Windows", 5th
Edition, we have the following listing:

/*-----------------------------------------------------
SCRNSIZE.C -- Displays screen size in a message box
(c) Charles Petzold, 1998
-----------------------------------------------------*/

#include <windows.h>
#include <tchar.h>
#include <stdio.h>

int CDECL MessageBoxPrintf (TCHAR * szCaption, TCHAR * szFormat, ...)
{
TCHAR szBuffer [1024] ;
va_list pArgList ;

// The va_start macro (defined in STDARG.H) is usually
equivalent to:
// pArgList = (char *) &szFormat + sizeof (szFormat) ;

va_start (pArgList, szFormat) ;

// The last argument to wvsprintf points to the arguments

_vsntprintf (szBuffer, sizeof (szBuffer) / sizeof (TCHAR),
szFormat, pArgList) ;

// The va_end macro just zeroes out pArgList for no good reason

va_end (pArgList) ;

return MessageBox (NULL, szBuffer, szCaption, 0) ;
}

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow)
{
int cxScreen, cyScreen ;

cxScreen = GetSystemMetrics (SM_CXSCREEN) ;
cyScreen = GetSystemMetrics (SM_CYSCREEN) ;
MessageBoxPrintf (TEXT ("ScrnSize"),
TEXT ("The screen is %i pixels wide by %i pixels
high."),
cxScreen, cyScreen) ;
return 0 ;
}

I'm able to compile this with VC++ 7.1 without defining the UNICODE
macro. However, when I define this macro, it does not compile. I get the
following error:

error C2664: '_vsnprintf' : cannot convert parameter 1 from 'TCHAR
[1024]' to 'char *'
Types pointed to are unrelated; conversion requires
reinterpret_cast, C-style cast or function-style cast

AFAICS, it should compile. Any ideas as to why this is happening?

Thanks,
Sumit.

 

[Carl Daniel [VC++ MVP]]

I'm able to compile this with VC++ 7.1 without defining the UNICODE
macro. However, when I define this macro, it does not compile. I get
the following error:

error C2664: '_vsnprintf' : cannot convert parameter 1 from 'TCHAR
[1024]' to 'char *'
Types pointed to are unrelated; conversion requires
reinterpret_cast, C-style cast or function-style cast

AFAICS, it should compile. Any ideas as to why this is happening?

You need to define _UNICODE to get the wide-character definition of
_vsntprintf.

-cd