UDN_DELTAPOSUDN_DELTAPOS*
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UDN_DELTAPOS


UDN_DELTAPOS 
    lpnmud = (LPNMUPDOWN) lParam;

Sent by the operating system to the parent window of an up-down control when the position of the control is about to change. This happens when the user requests a change in the value by pressing the control's up or down arrow. The UDN_DELTAPOS message is sent in the form of a WM_NOTIFY message.

lpnmud
Address of an NMUPDOWN structure that contains information about the position change.

The iPos member of this structure contains the current position of the control. The iDelta member of the structure is a signed integer that contains the proposed change in position. If the user has clicked the up button, this is a positive value. If the user has clicked the down button, this is a negative value.

The UDN_DELTAPOS notification is sent before the WM_VSCROLL or WM_HSCROLL message, which actually changes the control's position. This lets you examine, allow, modify, or disallow the change.

See also WM_COMMAND

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