Casting ? (C Conversion)

[Jim Warrick]

I'm playing around with the ImgSource dll and ran into a "C"
snag concerning pointers.
C Code:
// To get a pointer to the data, cast the HGLOBAL hImg to a BYTE*
BYTE *pRGB = (BYTE *) hImg;
It appears to be defining pRGB as a BYTE pointer, but whats going
on with the casting? Any help would be appreciated.
Yeah, I'm in over my head, but its fun!
Jim Warrick


------------------

[Tom Hanlin]

No special casting is necessary in PowerBASIC. LONG, DWORD, and PTR
types are compatible. You'll end up with something like this:

   LOCAL hImg AS DWORD
   LOCAL pRGB AS BYTE PTR
 
   pRGB = hImg

------------------
Tom Hanlin
PowerBASIC Staff

[Peter P Stephensen]

You have to cast, because

    BYTE *pRGB = hImg;

would generate an error. If you translate to PB,
then you dont need to caste: This is ok

    local pRGB as byte pointer : pRGB = hImg

Regards
Peter

------------------
[email protected]
www.dreammodel.dk

[Jim Warrick]

Thank you Tom and Peter for your replies. I'll give a shot.

Jim Warrick

------------------

[Borje Hagsten]

In case that won't work - I often encounter strange descriptions in C++
that turns out they were referring to a handle to memory, and so I have
to GlobalLock to get pointer to data.

Thought I'd tell, in case they wrote "cast" but meant something else,
like "lock". Is not unusual that happens..


------------------
http://www.tolkenxp.com/pb
Download: incLean, PBcodec, custom controls and code, etc.
Borje Hagsten - [email protected]

[Jim Warrick]

Thanks, Borje. I'll get back into the project this morning and
check it out.

Jim Warrick

------------------

[Michael Mattias]

I often encounter strange descriptions in C++ ...that turns out they were referring to a handle to memory, and so I have to GlobalLock to get pointer to data

That's more the 'C' programmer being 'cute' than anything else.

There is a set of flags you can use with GlobalAlloc (GHND?) which resulst in GlobalAlloc returning a pointer rather than a handle. "If" you use those flags for GlobalAlloc, you get away with this. (And I "think" you always get away with using the handle as a pointer under Win 9x/ME, but not so under Win NT/2K/XP.)

But it costs nothing and always works to use GlobalLock/GlobalUnlock on whatever is returned by GlobalAlloc.

MCM