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[eMTee <2019492@xxxxxxxxxxxxxxxxxx>]

Seems like the current available Win32 API documentation is inaccurate
and / or incomplete regarding how to pass extra data properly using
TCM_SETITEMEXTRA message and TCITEMHEADER structure.

First of all (as people also noted in a few other online forums), for
TCITEMHEADER the TCIF_PARAM flag in "mask" parameter must be set the
same way as in <https://learn.microsoft.com/en-
us/windows/win32/api/commctrl/ns-commctrl-tcitema#members> when used for
getting or setting a tab item's data. <https://learn.microsoft.com/en-
us/windows/win32/api/commctrl/ns-commctrl-tcitemheadera#members> omits
this information.

Secondly, unlike the way documented in <https://learn.microsoft.com/en-
us/windows/win32/api/commctrl/nf-commctrl-tabctrl_setitemextra> the
TabCtrl_SetItemExtra macro indeed has a success/failure return value, it
is clear from CommCtrl.h.

And finally, the data size requirement when one wants to pass extra data
using TCITEMHEADER is inaccurately documented as well.
<https://learn.microsoft.com/en-us/windows/win32/controls/tcm-
setitemextra#remarks> says "By default, the number of extra bytes is
four." which is valid for 32-bit apps/calls only. In 64-bit apps this
default size appears to be 8 bytes since if you set this size by sending
a TCM_SETITEMEXTRA message then it is silently discarded and things fall
back to the old way when TCITEM is used: you get a 4-byte-long truncated
value again when getting tab info and the same wrong _value_ passed
through messages containing DRAWITEMSTRUCTs (and not reference to the
extra data, as described in <https://learn.microsoft.com/en-
us/windows/win32/controls/tab-controls?redirectedfrom=MSDN#owner-drawn-
tabs>).

As a workaround, to avoid the extra data size to be either 4 or 8, a
dummy byte is added to the extra data structure which makes things work
in both architectures.


** Changed in: dcplusplus
       Status: Confirmed => Fix Committed

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Dcplusplus-team, which is a bug assignee.
https://bugs.launchpad.net/bugs/2019492

Title:
  Tab control crash Win10+

Status in DC++:
  Fix Committed

Bug description:
  When running DC++ compiled under MSVC (Currently using VS2022) and
  running on Win10+ DC++ will crash when using OwnerDrawn tabs and
  selecting button style which will cause DC++ to immediately crash in
  TabView->handlePainting (You can force this crash on every startup by
  going into DCPlusPlus.xml and setting the following <TabStyle
  type="int">6</TabStyle>.

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