How to use GetKeyState()

Code:

---

WORD keyState;
//.............
keyState = GetKeyState(VK_SHIFT);
                if(HIWORD(keyState) & 0x80)
                {
                        MessageBox(NULL, TEXT("SHIFT Down"), TEXT("Key State"), MB_OK);
                }

---

Not sure how to go about detecting whether the hi order bit is 1...which is what I need D:

-edit-
ok nm I got it

Code:

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if(GetKeyState(VK_SHIFT) & 0x80)
                {
                        MessageBox(NULL, TEXT("SHIFT Down"), TEXT("Key State"), MB_OK);
                }

---

The return value of GetKeyState is a short what normally is a 16-bit integer. Hence, the short which has a bit combination where only the highest bit is set is '1000000000000000' binary or 0x8000 hex. The samples often use macro HIWORD which extracts the high 8 bits of the short, i. e. '10000000' binary or 0x80 hex. By doing a binary & operation on the return value with that you can test whether the bit was set cause 'AND' would only return non-zero when both operands have the same bit position set to 1 for at least 1 bit.

So

Code:

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if ((keyState & 0x8000) != 0)

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or

Code:

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if ((HIWORD(keyState) & 0x80) != 0)

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both are testing if the highest bit was set in keyState (which must be a short).

Sorry, but GetKeyState() returns a SHORT (16-bit) and HIWORD() returns the uppermost 16 bits of a DWORD (i.e. 32-bit value). I didn't actually look at the definition of that macro but I would expect that applying HIWORD() to the SHORT returned by GetKeyState() would return 0 in all cases.

If necessary at all (here itsmeandnobodyelse is right), the applicable macro here would be HIBYTE().

EDIT: Oh, wait... :o If, wehn passed to the HIWORD() macro, the signed 16-bit SHORT would be converted to an unsigned 32-bit DWORD using sign extension, using HIWORD() here actually would give the correct result, though achieved in an uncorrect way.

Quote:

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Originally Posted by Eri523

EDIT: Oh, wait... :o If, wehn passed to the HIWORD() macro, the signed 16-bit SHORT would be converted to an unsigned 32-bit DWORD using sign extension, using HIWORD() here actually would give the correct result, though achieved in an uncorrect way.

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Double Nope.

Keystate is here declared as a WORD (even though GetKeyState() returns a short), so it won't get sign extended into a DWORD. It'll be zero-extended.

If keystate would have been declared as a signed short, the example wouldn't work properly. It would sign-extend, but in that case HIWORD(shortVal) will be 0xFFFF.


Due to compiler optimisations, the HIBYTE(keyState)&0x80 will be slightly more optimal.