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LOWORD/HIWORD vs GET_X_LPARAM/GET_Y_LPARAM and MAKELONG vs MAKELPARAM

Posted on 2013-11-28
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Last Modified: 2013-11-29
Hi!

While searching for something else, I ran across the statement that in Windows functions interpreting coordinates, one should use GET_X_LPARAM/GET_Y_LPARAM instead of LOWORD/HIWORD on the lParam parameter. Also it seems one should use MAKELPARAM instead of MAKELONG.

I do understand the difference, but feel a little uncertain about the benefits and pitfalls by simply replacing:

- LOWORD -> GET_X_LPARAM
- HIWORD -> GET_Y_LPARAM
- MAKELONG -> MAKELPARAM

in all of my company's code.

First about the need to do this: is it correct that the only problem with not changing this is that things might (or certainly will?) not work if your multiple monitor setup is different from having the main monitor to the left and others as extensions to the right of it?

Or does it even then work as long as you avoid some very specific functions?

Then to the pitfalls: if we simply do the replacements above in all our code, is there any reason to believe something that works correct now doesn't work the same afterwards?

I am guessing not, but I would like to be very sure before I suggest such a change in all our code.

Thank you for any insight into this!
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Question by:khun
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tedbilly earned 250 total points
ID: 39684757
It will definitely cause problems with many functions if there are multiple monitors.  There is no harm to making the change.  I'd do it.
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by:sarabande
sarabande earned 250 total points
ID: 39684806
#define GET_X_LPARAM(lp)  ((int)(short)LOWORD(lp))

Open in new window

in vs2010 both macros are identically beside that the result is int or short. because of that you could use the GET_X_LPARAM if you don't use short (16-bit) integers.

generally all those macros are helpers only. you can trust that for existing API the results will not change. for new api things are different. for example LPARAM turned to a 64-bit integer type what allows to pass a 64-bit pointer (address). for newer code you probably would avoid bit masking and pass pointers or handles which may point to larger objects and structures. then you would not use those macros at all but use your own functions to resolve the parameters.

Sara
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by:khun
ID: 39684865
Actually, I have now tested with some weird 2 monitor setups and confirmed that HIWORD/LOWORD don't work correctly! I'll go for a global replace in all our code.

Thanks for the input reassuring me that this is risk free and necessary!
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