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CHANGEFILTERSTRUCT structure (winuser.h)

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Contains extended result information obtained by calling the ChangeWindowMessageFilterEx function.

Syntax

typedef struct tagCHANGEFILTERSTRUCT {
  DWORD cbSize;
  DWORD ExtStatus;
} CHANGEFILTERSTRUCT, *PCHANGEFILTERSTRUCT;

Members

cbSize

Type: DWORD

The size of the structure, in bytes. Must be set to sizeof(CHANGEFILTERSTRUCT), otherwise the function fails with ERROR_INVALID_PARAMETER.

ExtStatus

Type: DWORD

If the function succeeds, this field contains one of the following values.

Value Meaning
MSGFLTINFO_NONE
0
 See the Remarks section. Applies to MSGFLT_ALLOW and MSGFLT_DISALLOW.
MSGFLTINFO_ALLOWED_HIGHER
3
 The message is allowed at a scope higher than the window. Applies to MSGFLT_DISALLOW.
MSGFLTINFO_ALREADYALLOWED_FORWND
1
 The message has already been allowed by this window's message filter, and the function thus succeeded with no change to the window's message filter. Applies to MSGFLT_ALLOW.
MSGFLTINFO_ALREADYDISALLOWED_FORWND
2
 The message has already been blocked by this window's message filter, and the function thus succeeded with no change to the window's message filter. Applies to MSGFLT_DISALLOW.

Remarks

Certain messages whose value is smaller than WM_USER are required to pass through the filter, regardless of the filter setting. There will be no effect when you attempt to use this function to allow or block such messages.

An application may use the ChangeWindowMessageFilter function to allow or block a message in a process-wide manner. If the message is allowed by either the process message filter or the window message filter, it will be delivered to the window.

The following table lists the possible values returned in ExtStatus.

Message already allowed at higher scope Message already allowed by window's message filter Operation requested Indicator returned in ExtStatus on success
No No MSGFLT_ALLOW MSGFLTINFO_NONE
No No MSGFLT_DISALLOW MSGFLTINFO_ALREADYDISALLOWED_FORWND
No No MSGFLT_RESET MSGFLTINFO_NONE
No Yes MSGFLT_ALLOW MSGFLTINFO_ALREADYALLOWED_FORWND
No Yes MSGFLT_DISALLOW MSGFLTINFO_NONE
No Yes MSGFLT_RESET MSGFLTINFO_NONE
Yes No MSGFLT_ALLOW MSGFLTINFO_NONE
Yes No MSGFLT_DISALLOW MSGFLTINFO_ALLOWED_HIGHER
Yes No MSGFLT_RESET MSGFLTINFO_NONE
Yes Yes MSGFLT_ALLOW MSGFLTINFO_ALREADYALLOWED_FORWND
Yes Yes MSGFLT_DISALLOW MSGFLTINFO_ALLOWED_HIGHER
Yes Yes MSGFLT_RESET MSGFLTINFO_NONE

Requirements

Requirement Value
Minimum supported client Windows 7 [desktop apps only]
Minimum supported server Windows Server 2008 R2 [desktop apps only]
Header winuser.h (include Windows.h)

See also

ChangeWindowMessageFilterEx