Samuel's OS/2 Programming Tricks

By Samuel Audet

Last Modified: March 1, 2005

Autodetecting installed CD-ROM drive letters

There is a way to autodetect the CD-ROM drive letter through undocumented ioctls, even though I heard they may have come from the DDK.

HFILE CDDevice;
ULONG action;
ULONG len;
struct
{
    USHORT CountCD;
    USHORT FirstCD;
} CDInfo;

len = sizeof(CDInfo);
if(!DosOpen("\\DEV\\CD-ROM2$", &CDDevice, &action, 0,
            FILE_NORMAL, OPEN_ACTION_OPEN_IF_EXISTS,
            OPEN_SHARE_DENYNONE | OPEN_ACCESS_READONLY, NULL))
{
   if(!DosDevIOCtl(CDDevice, 0x82, 0x60, NULL, 0, NULL, &CDInfo, len, &len))
   {
      for(i = 0; i < CDInfo.CountCD; i++)
      {
         char driveLetter[3] = { (char) ('A' + CDInfo.FirstCD + i), ':', 0};
         /* got one drive letter in driveLetter, use it */
      }
   }
   DosClose(CDDevice);
}

Making a program find its own directory

This's one is a bit tricky, but it's pretty obvious once you know how.

ULONG PathLength;
char *Path;

/* query max path length */

if (!DosQuerySysInfo(QSV_MAX_PATH_LENGTH, QSV_MAX_PATH_LENGTH, &PathLength, sizeof(ULONG)))
   Path = (char *) malloc(2*PathLength*sizeof(char)+1);

/* multiplied by 2 to include the filename length too */

if(Path)
{
   PPIB ppib;
   PPIT ppit;

   DosGetInfoBlocks(&ppit, &ppib);
   DosQueryModuleName(ppib->pib_hmte, 2*PathLength+1, Path);

   *(strrchr(Path,'\\')) = 0;

   Path = (char *)realloc(Path, (strlen(Path)+1)*sizeof(char));

   /* got the path in Path, use it */
}

Notebook dialogs

So, what would you like to do with Notebook dialogs?

• Easily Load and Manage Pages
• Making Help Manager Useable

WinHSWITCHfromHAPP()

This function is hidden in PMSHAPI.DLL, and you can import it in any of your programs (in the DEF file using "IMPORTS PMSHAPI.WINHSWITCHFROMHAPP" for example). The C syntax is:

HSWITCH APIENTRY16 WINHSWITCHFROMHAPP(HAPP happ);

Doesn't seem useful? Guess what is the "open handle" of the VIEWITEM and VIEWFILE structure. You got it... You can then do whatever you are used to doing with an HSWITCH.

And you can do some pretty amazing things with this and WinStartApp(). Makes me wonder what WinStartApp() really does, as DosStartSession() doesn't do half of what you can find with those.

Note however that for WPS windows, "open handle" is a window handle, so try to use it as a window handle, if it fails, use WINHSWITCHFROMHAPP().

Thanks to Uri Joseph Stern for this one, I needed it dearly.

Checking the class of a window handle

Ok, here's the trick:

(example, if you want to know if hwnd is a scroll bar)

CHAR achClass[256]

WinQueryClassName(hwnd,sizeof(achClass),achClass);
if(WinFindAtom(WinQuerySystemAtomTable(),achClass)
   == LOUSHORT(WC_SCROLLBAR))
   /* this is a scroll bar */;
else
   /* this is not a scroll bar */;

Thanks to Larry Salomon Jr. in EDM/2 and to Robert Mahoney for letting me know about it.

Masking File Names in Strings

fnmatch.zip - 5 kB

This is a wildcard string matcher that I "ported" from EMX to VisualAge C++ (although source codes are included). I have replaced EMX functions with VAC++ equivalents, and I have stripped out DBCS support, since, euh, I didn't know how to support it in VAC++.

The advantage of this routine over Dos*() API filename wildcard matcher is that you don't need an actual file to match a wildcard, you only need two strings. This can be very useful in many situations.

Hooks and the Workplace Shell

If you plan on using hooks from the Workplace Shell, make sure you make one DLL for the WPS Class and another DLL for the hook. I learned the hard way that a hook from a WPS DLL just doesn't work right (God knows why).

Leaving Hooks loaded after program execution

You can leave a hook loaded any time after a program has finished executing. In theory, you would only need not execute WinReleaseHook(), but it seems WinSetHook() executes asynchronously from the calling program. There must be a better way to know when the hook is loaded, but here's how I do it (this requires a shared memory segment or a single stack DLL):

In the Hook DLL, I have this code:

BOOL loaded = FALSE;

BOOL EXPENTRY WinHookProc(HAB hab,PQMSG pqmsg, USHORT usRemove)
{
   loaded = TRUE;
   ...
}

BOOL EXPENTRY WaitLoaded(void)
{
   while(!loaded) DosSleep(10);
   return TRUE;
}

In the hook loader, I call WaitLoaded() before returning from the main() function. Note that this only seems to work for VIO executables... :( An example of this is in numcomma.zip (31 kB).

Scroll Bars "style"

If you ever need to check if a scroll bar is horizontal or vertical, check with SBS_VERT first (or only) since SBS_HORZ is actually set to 0 in PMWIN.H, which will always make an if statement fail. i.e.:

if(WinQueryWindowULong(hwndscroll,QWL_STYLE) & SBS_VERT)
   /* this is a vertical scroll bar */;
else
   /* this is a horizontal scroll bar */;

and NOT

if(WinQueryWindowULong(hwndscroll,QWL_STYLE) & SBS_HORZ)
   /* this is a horizontal scroll bar */;
else
   /* this is a vertical scroll bar */;