CreateDetourAtDLLEntry

Detours a function of a loaded DLL, found by the names of the DLL and the function, and returns the address that calls the original function.

Syntax: CreateDetourAtDLLEntry ( libName, funcName, newAddress ) As LongPtr

libName
required A String, the name of a DLL that the process has already loaded, such as "user32" or "user32.dll". A name without an extension means a .dll file.
funcName
required A String, the name under which the DLL exports the function, such as "SetFocus" or "MessageBoxW". The name is case-sensitive.
newAddress
required A LongPtr, the address of the detour, usually AddressOf and the name of a procedure in a module.

Returns the address of the trampoline, which calls the original function. It is not the function’s own address: a call to the function goes to the detour, and a call through the returned address runs the original. Keep the address for as long as the detour is in place, convert it to a Delegate type to call the original, and pass it to RemoveDetour to remove the detour.

The function finds the DLL with the GetModuleHandle API and the function with GetProcAddress, then places the detour with SlimDetoursInlineHook, as CreateDetourAtFuncAddress does. It does not load the DLL.

Note 1.0.0.0

The DLL must already be loaded in the process, or the function raises error 5, CreateDetourAtDLLEntry libName: DLL library not found. To detour a function of a DLL that may not be loaded yet, load the DLL first with the LoadLibrary API.

Errors lists the errors the function raises.

Example

This module detours SetFocus of user32 so that the program can see which window each call gives the focus to.

Private Delegate Function SetFocusFn (ByVal hWnd As LongPtr) As LongPtr
Private RealSetFocus As SetFocusFn

Private Function MySetFocus(ByVal hWnd As LongPtr) As LongPtr
    Debug.Print "SetFocus &H"; Hex(hWnd)
    Return RealSetFocus(hWnd)
End Function

Public Sub WatchFocus()
    RealSetFocus = CType(Of SetFocusFn)(CreateDetourAtDLLEntry("user32", "SetFocus", AddressOf MySetFocus))
End Sub

Public Sub StopWatchingFocus()
    RemoveDetour RealSetFocus, AddressOf MySetFocus
End Sub

See Also