SetTextColor return values

[UtillMasm]

 :eek
i hate protect my ECX before INVOKE SetTextColor.

Code Select Expand

invoke SetTextColor,HandleOfDC,Color
then return values:

Code Select Expand

eax
ecx
What is mean the ECX value?

[jj2007]

:eek
i hate protect my ECX before INVOKE SetTextColor.

Code Select Expand

invoke SetTextColor,HandleOfDC,Color
then return values:

Code Select Expand

eax
ecx
What is mean the ECX value?

If the function succeeds, the return value is a color reference for the previous text color

Return value is always eax, unless explicitly specified differently. Ecx and edx are usually garbage, i.e. the OS uses them for own purposes and doesn't bother to save the original values.

[UtillMasm]

 :U
ECX is garbage.

[jj2007]

:U
ECX is garbage.

... if coming out of a Window API. Otherwise, it's a versatile register that has a specific role in instructions such as rep xxx, jecxz, loopz etc.; that's why I chose to preserve it in MasmBasic. It is a matter of taste, eh, convention, and those who invented the ABI chose to trash it. Bad luck. If you need a workaround:

Code Select Expand

invapi MACRO api, args:VARARG
  push ecx
  push edx  ; optional. Per push/pop pair, count 2 bytes and 1-2 cycles
  ifb <args>
call api
  else
invoke api, args
  endif
  pop edx
  pop ecx
ENDM


Usage:

Code Select Expand

start:
mov ecx, 123
mov edx, 456
invapi GetTickCount
push edx   ; print trashes ecx and edx, too...
print str$(ecx), " "
pop edx
print str$(edx), 13, 10

mov ecx, 123
mov edx, 456
invapi Sleep, 1000
push edx
print str$(ecx), " "
pop edx
print str$(edx), 13, 10



[sinsi]

When you call an API there are registers that are preserved - EBX,ESI,EDI,EBP - and those that are trashed (undefined) - ECX,EDX.
Trashed as well is EAX if the API call doesn't return a value (but that's pretty rare).

This means that if you have a callback function you need to preserve the same registers windows does - EBX,ESI,EDI,EBP. I'm pretty sure this includes your window procedure.

[UtillMasm]

 :U

i really love jj's Incredible MACRO Functions.

JJ:

sir, when you release RichMasm source? :wink