newbie question windows programming

[gemini_shooter]

Hi!

I am just starting to learn windows programming and picked up my first book "programming Windows" 5th ediion by charles petzold to start from the very basics, but I got stuck at the 2nd program. This is a program from the bookand I tried to install it on VC++ 6. The program compiles fine but does not link and give me some error.

The program is:

/*-----------------------------------------------------
   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 ;
}

The error that I get is :

--------------------Configuration: ScrnSize - Win32 Debug--------------------
Linking...
LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
Debug/ScrnSize.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

ScrnSize.exe - 2 error(s), 0 warning(s)

Since I am still at the 2nd chapter of this book I am little confused on why this is not linking

Also the I need a dumbed out version of how the variables cxScreen and cyScreen give there values to messagebox function or in otherwords I didn't understand what this line is doing :

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

any help would be great !!!

[r1ck0r]

The reason you are getting those linker errors is because you have created a 'win32 console application' project. you must create a 'win32 application' project. Once you have done that, it will compile fine.

[Jaken Veina]

Yep. A Win32 Console project is just about anything in C or C++ other than windows programming. If you did anything in C or C++ before going to windows, and your program ran from a black backgrounded window, that was a Console Application. Since you're working with windows, you don't want that console. If there is a "Project Options" item under your menu somwhere, you'll be able to change the project type there.

[gemini_shooter]

sorry about the double post !!!

Thanks for pointing out my mistake. but also I still don't understand what does this line actually do

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

[TheColonial]

First, read up on the _vsntprintf() function, and then do some reading on variable arguments. It will become clear. Also, if you know how printf() works, you might learn a bit by looking under the hood of the printf function