Calling a function using variable name in VBA - vba

Question

Thanks in advance.
I'm trying to call a function using a variable name. It's throwing the error
The macro 'testfunc' cannot be found.
Resume without error
My Code: I tried below 3 statements but all are throwing the same error.
sFuncName = "testfunc"
ExtractData = Application.Run("Sheet.xls" & sFuncName, s1, s2)
ExtractData = Application.Run(sFuncName, s1, s2)
ExtractData = CallByName("Sheet.xls", sFuncName, VbMethod, s1, s2)
Note that the sFuncName returns a value & I have 2 Excels opened at that moment, I'm trying to copy data from one Excel to other.
Please help me in achieving this.
Private Function ABC
sFuncName = oMapWksht.Cells(sMapRowItr, 3).Value
'sFuncName = "testfunc"
ExtractData = Application.Run("Sheet.xls" & sFuncName, s1, s2)
'ExtractData = Application.Run(sFuncName, s1, s2)
'ExtractData = CallByName("Sheet.xls", sFuncName, VbMethod, s1, s2)
End Function
Public Function testfunc(ByVal s1 As String, ByVal s2 As String) As Boolean
--
---
----
End Function

Answer 1

If the function you're calling is in the same workbook as the caller, it doesn't matter how many workbooks are opened.
If the invoked procedure doesn't have a unique name across the entire project, you need to qualify the function name with at least the name of the module though. This should get you going:
Module1 (caller)
Sub DoSomething()
Debug.Print Application.Run("Module2.Test", "Test")
End Sub
Module2 (callee)
Public Function Test(ByVal title As String) As VbMsgBoxResult
Test = MsgBox("Works?", vbQuestion + vbYesNo, title)
End Function

Answer 2

You can use a String variable to hold the Sub's name. Here is an example of a Sub in the same module as the caller:
Sub MAIN()
Dim st As String
st = "whatever"
Application.Run st
End Sub
Public Sub whatever()
MsgBox "whatever"
End Sub
If the caller and called subs are in different modules, the syntax may be slightly different.
EDIT#1:
If we want to call a Sub in a different module within the same workbook, the syntax would be the same.
If we want to call a Sub within another workbook, and both workbooks are open then the caller would look like:
Sub MAIN()
Dim st As String
st = "Book2.xlsm!whatever"
Application.Run st
End Sub
I usually declare the called Sub Public, but I don't know if this is necessary.
EDIT#2
To use another workbook's UDF() in a worksheet cell, then:
where qwerty() is a Public UDF()