C# Signature:

[DllImport("user32.dll", SetLastError=true, CharSet=CharSet.Auto)]
static extern IntPtr SendMessageTimeout(IntPtr hWnd, uint Msg,
   UIntPtr wParam, string lParam, SendMessageTimeoutFlags fuFlags,
   uint uTimeout, out UIntPtr lpdwResult);

User-Defined Types:

[[Flags]]

public enum SendMessageTimeoutFlags:uint

{

    SMTO_NORMAL=  0x0000
    , SMTO_BLOCK = 0x0001
    , SMTO_ABORTIFHUNG =  0x0002
    , SMTO_NOTIMEOUTIFNOTHUNG = 0x0008

}

Notes:

None.

Tips & Tricks:

Changed the IntPtr lParam to string lParam to enable the possibility to use a string as input.

Sample Code:

//Notify all windows that User Environment variables are changed

IntPtr HWND_BROADCAST = (IntPtr) 0xffff;

const UInt32 WM_SETTINGCHANGE = 0x001A;

UIntPtr result;

IntPtr settingResult = SendMessageTimeout(HWND_BROADCAST,

WM_SETTINGCHANGE,

(UIntPtr)0,

"Environment",

SendMessageTimeoutFlags.SMTO_NORMAL,

10000,

out result);

Alternative Managed API:

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