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Quick Info
Windows NT
| Yes
| Win95
| Yes
| Win32s
| Yes
| Import Library
| user32.lib
| Header File
| winuser.h
| Unicode
| WinNT
| Platform Notes
| None
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PostThreadMessage
The PostThreadMessage function places (posts) a message in the message queue of the specified
thread and then returns without waiting for the thread to process the message.
BOOL PostThreadMessage(
DWORD idThread,
| // thread identifier
| UINT Msg,
| // message to post
| WPARAM wParam,
| // first message parameter
| LPARAM lParam
| // second message parameter
| );
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Parameters
idThread
Identifies the thread to which the message will be posted.
The function fails if the specified thread does not have a message queue. The
system creates a thread's message queue when the thread makes its first call to
one of the Win32 USER or GDI functions. For more information, see the Remarks
section.
Msg
Specifies the type of message to be posted.
wParam
Specifies additional message-specific information.
lParam
Specifies additional message-specific information.
Return Values
If the function succeeds, the return value is nonzero.
If the function fails, the return value is zero. To get extended error
information, call GetLastError. GetLastError returns ERROR_INVALID_THREAD_ID if idThread is not a valid thread identifier, or if the thread specified by idThread does not have a message queue.
Remarks
The thread to which the message is posted must have created a message queue,
or else the call to PostThreadMessage fails. Use one of the following methods to handle this situation:
- Call PostThreadMessage. If it fails, call the Sleep function and call PostThreadMessage again. Repeat until PostThreadMessage succeeds.
- Create an event object, then create the thread. Use the WaitForSingleObject function to wait for the event to be set to the signaled state before calling PostThreadMessage. In the thread to which the message will be posted, call PeekMessage(&msg, NULL, WM_USER, WM_USER, PM_NOREMOVE) to force the system to create the
message queue. Set the event, to indicate that the thread is ready to receive
posted messages.
The thread to which the message is posted retrieves the message by calling the GetMessage or PeekMessage function. The hwnd member of the returned MSG structure is NULL.
See Also
GetCurrentThreadId, GetMessage, GetWindowThreadProcessId, MSG, PeekMessage, PostMessage, Sleep, WaitForSingleObject
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Unix Manual Pages
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