GETMESSAGE hook, WM_SYSCOMMAND, SC_CLOSE, and the "X" button?

[Vincent Fatica]

In an extension (DLL) to a subsystem:windows app I'm trying to make the app hard
to close. A simple WH_GETMESSAGE hook correctly sees <WM_SYSCOMMAND, SC_CLOSE>
when it's generated by the system menu's "Close" (also <Alt-F4>) and translates
it into <WM_SYSCOMMAND, SC_MINIMIZE>. But my hook fails to see <WM_SYSCOMMAND,
SC_CLOSE> when it was generated by the title bar's "X" button. The application
does not set any other hooks.

What's going on here? Can I work around it?

Thanks.

[Igor Tandetnik]

Post by Vincent Fatica
In an extension (DLL) to a subsystem:windows app I'm trying to make
the app hard to close. A simple WH_GETMESSAGE hook correctly sees
<WM_SYSCOMMAND, SC_CLOSE> when it's generated by the system menu's
"Close" (also <Alt-F4>) and translates it into <WM_SYSCOMMAND,
SC_MINIMIZE>. But my hook fails to see <WM_SYSCOMMAND, SC_CLOSE>
when it was generated by the title bar's "X" button. The application
does not set any other hooks.

Have you seen the part of WM_SYSCOMMAND documentation that says:

To obtain the correct result when testing the value of wParam, an
application must combine the value 0xFFF0 with the wParam value by using
the bitwise AND operator.

Are you doing this?

[Vincent Fatica]

Post by Igor Tandetnik

Post by Vincent Fatica
In an extension (DLL) to a subsystem:windows app I'm trying to make
the app hard to close. A simple WH_GETMESSAGE hook correctly sees
<WM_SYSCOMMAND, SC_CLOSE> when it's generated by the system menu's
"Close" (also <Alt-F4>) and translates it into <WM_SYSCOMMAND,
SC_MINIMIZE>. But my hook fails to see <WM_SYSCOMMAND, SC_CLOSE>
when it was generated by the title bar's "X" button. The application
does not set any other hooks.

To obtain the correct result when testing the value of wParam, an
application must combine the value 0xFFF0 with the wParam value by using
the bitwise AND operator.
Are you doing this?

No I wasn't. Thanks. I tried it. It didn't help.