C# Signature:

// This helper static method is required because the 32-bit version of user32.dll does not contain this API
// (on any versions of Windows), so linking the method will fail at run-time. The bridge dispatches the request
// to the correct function (GetWindowLong in 32-bit mode and GetWindowLongPtr in 64-bit mode)
public static IntPtr SetWindowLongPtr(HandleRef hWnd, int nIndex, IntPtr dwNewLong)
{
      if (IntPtr.Size == 8)
      return SetWindowLongPtr64(hWnd, nIndex, dwNewLong);
      else
      return new IntPtr(SetWindowLong32(hWnd, nIndex, dwNewLong.ToInt32()));
}

[DllImport("user32.dll", EntryPoint="SetWindowLong")]
private static extern int SetWindowLong32(HandleRef hWnd, int nIndex, int dwNewLong);

[DllImport("user32.dll", EntryPoint="SetWindowLongPtr")]
private static extern IntPtr SetWindowLongPtr64(HandleRef hWnd, int nIndex, IntPtr dwNewLong);

/// <summary>
/// Changes an attribute of the specified window. The function also sets the 32-bit (long) value at the specified offset into the extra window memory.
/// </summary>
/// <param name="hWnd">A handle to the window and, indirectly, the class to which the window belongs..</param>
/// <param name="nIndex">The zero-based offset to the value to be set. Valid values are in the range zero through the number of bytes of extra window memory, minus the size of an integer. To set any other value, specify one of the following values: GWL_EXSTYLE, GWL_HINSTANCE, GWL_ID, GWL_STYLE, GWL_USERDATA, GWL_WNDPROC </param>
/// <param name="dwNewLong">The replacement value.</param>
/// <returns>If the function succeeds, the return value is the previous value of the specified 32-bit integer.
/// If the function fails, the return value is zero. To get extended error information, call GetLastError. </returns>
[DllImport("user32.dll")]
static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

VB.NET Signature:

  <System.Runtime.InteropServices.DllImport("user32.dll", EntryPoint:="SetWindowLong")> _
  Private Shared Function SetWindowLong32(ByVal hWnd As IntPtr, <MarshalAs(UnmanagedType.I4)>nIndex As WindowLongFlags, ByVal dwNewLong As Integer) As Integer
  End Function

  <System.Runtime.InteropServices.DllImport("user32.dll", EntryPoint:="SetWindowLongPtr")> _
  Private Shared Function SetWindowLongPtr64(ByVal hWnd As IntPtr, <MarshalAs(UnmanagedType.I4)>nIndex As WindowLongFlags, ByVal dwNewLong As IntPtr) As IntPtr
  End Function

  Public Shared Function SetWindowLongPtr(ByVal hWnd As IntPtr, nIndex As WindowLongFlags, ByVal dwNewLong As IntPtr) As IntPtr
    If IntPtr.Size = 8 Then
      Return SetWindowLongPtr64(hWnd, nIndex, dwNewLong)
    Else
      Return New IntPtr(SetWindowLong32(hWnd, nIndex, dwNewLong.ToInt32))
    End If
  End Function

VB.NET Signature:

Public Declare Function SetWindowLongPtr Lib "user32" Alias "SetWindowLongPtrA" _
<DllImport("user32.dll")> _
Private Shared Function SetWindowLong(hWnd As IntPtr, _
     <MarshalAs(UnmanagedType.I4)>nIndex As WindowLongFlags, _
     dwNewLong As IntPtr) As <MarshalAs(UnmanagedType.I4)>WindowLongFlags
End Function

VB Signature:

Public Declare Function SetWindowLong Lib "user32.dll" Alias "SetWindowLongA" _
        (ByVal hWnd As Long, _
         ByVal nIndex As WindowLongFlags, _
         ByVal dwNewLong As Long) As Long

         ByVal dwNewLong As Long) As WindowLongFlags

User-Defined Types:

WindowLongFlags

Alternative Managed API:

Do you know one? Please contribute it!

Notes:

The constants required to call this can be found in the constant section of this site.

None.

Tips & Tricks:

Please add some!

Certain window data is cached, so changes you make using SetWindowLong will not take effect until you call the SetWindowPos function. Specifically, if you change any of the frame styles, you must call SetWindowPos with the SWP_FRAMECHANGED flag for the cache to be updated properly.

Sample Code:

Please add some!

The following sample uses the GetWindowLong and SetWindowLong to remove the 3D border in the MDI client area.

    C# example
    int lStyle = user32.GetWindowLong(handle, WS.GWL_STYLE);
    lStyle &= ~(WS.WS_CAPTION | WS.WS_BORDER | WS.WS_DLGFRAME | WS.WS_SIZEBOX | WS.WS_THICKFRAME);
    user32.SetWindowLong(handle, WS.GWL_STYLE, lStyle);

Error in Windows 7 64 bit under Parallels on Mac, in Visual Studio Express 13 (Visual Basic Forms Application):

When called, the following error was given:

Additional information: Unable to find an entry point named 'SetWindowLongPtrA' in DLL 'user32'

...Geoff Kelly

    VB.net example
    Private Declare Auto Function SetWindowLong Lib "User32.Dll" (ByVal hWnd As IntPtr, ByVal nIndex As Integer, ByVal dwNewLong As Integer) As Integer
    Private Declare Auto Function GetWindowLong Lib "User32.Dll" (ByVal hWnd As System.IntPtr, ByVal nIndex As Integer) As Integer
    Private Const GWL_EXSTYLE = (-20)
    Private Const WS_EX_CLIENTEDGE = &H200

    Private Sub RemoveMdiBorder()

    For Each c As Control In Me.Controls
        If TypeOf c Is MdiClient Then
        Dim windowLong As Long = GetWindowLong(c.Handle, GWL_EXSTYLE)
        windowLong = windowLong And (Not WS_EX_CLIENTEDGE)
        SetWindowLong(c.Handle, GWL_EXSTYLE, windowLong)
        c.Width = c.Width + 1
        Exit For
        End If
    Next

    End Sub

Alternative Managed API:

Do you know one? Please contribute it!

The above signature is incorrect. The dwNewLong parameter must be an IntPtr, not an int, because the native function takes a DWORD (unsigned int), not an integer.

- This is not quite true: passing int and int32 into SetWindowLong does still work.

-- This functions takes a LONG as third argument and return type, and LONG is declared as a 32-bit signed integer. The function SetWindowLongPtr supersedes this function and has the LONG_PTR type for the third argument and return value. LONG_PTR is 32-bits for a 32-bits OS and 64-bits on a 64-bit OS.

- You should also be aware that a LONG in the .NET framework is defined as a 8-Byte (64-Bit) Integer! While the Integer (Int32) is defined as 4-Byte Integer.

Please edit this page!

Do you have...

• helpful tips or sample code to share for using this API in managed code?
• corrections to the existing content?
• variations of the signature you want to share?
• additional languages you want to include?

Select "Edit This Page" on the right hand toolbar and edit it! Or add new pages containing supporting types needed for this API (structures, delegates, and more).