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Processing varargin and varargout Arguments

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Overview Passing an Empty varargin from Microsoft Visual Basic Code

Overview

When varargin and/or varargout are present in the MATLAB function that you are using for the Excel component, these parameters are added to the argument list of the class method as the last input/output parameters in the list. You can pass multiple arguments as a varargin array by creating a Variant array, assigning each element of the array to the respective input argument.

The following example creates a varargin array to call a method resulting from a MATLAB function of the form y = foo(varargin):

Function foo(x1 As Variant, x2 As Variant, x3 As Variant, _
             x4 As Variant, x5 As Variant) As Variant
   Dim aClass As Object
   Dim v(1 To 5) As Variant
   Dim y As Variant 
   
   On Error Goto Handle_Error
   v(1) = x1
   v(2) = x2
   v(3) = x3
   v(4) = x4
   v(5) = x5
   aClass = CreateObject("mycomponent.myclass.1_0")
   Call aClass.foo(1,y,v)
   foo = y
   Exit Function
Handle_Error:
   foo = Err.Description
End Function

The MWUtil class included in the MWComUtil utility library provides the MWPack helper function to create varargin parameters. See Utility Library Classes for more details.

The next example processes a varargout parameter into three separate Excel Ranges. This function uses the MWUnpack function in the utility library. The MATLAB function used is varargout = foo(x1,x2).

Sub foo(Rout1 As Range, Rout2 As Range, Rout3 As Range, _
        Rin1 As Range, Rin2 As Range)
   Dim aClass As Object
   Dim aUtil As Object
   Dim v As Variant
    
   On Error Goto Handle_Error
   aUtil = CreateObject("MWComUtil.MWUtil")
   aClass = CreateObject("mycomponent.myclass.1_0")
   Call aClass.foo(3,v,Rin1,Rin2)
   Call aUtil.MWUnpack(v,0,True,Rout1,Rout2,Rout3)
   Exit Sub
Handle_Error:
   MsgBox(Err.Description)
End Sub

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Passing an Empty varargin from Microsoft Visual Basic Code

In MATLAB, varargin inputs to functions are optional, and may be present or omitted from the function call. However, from Microsoft Visual Basic, function signatures are more strict—if varargin is present among the MATLAB function inputs, the VBA call must include varargin, even if you want it to be empty. To pass in an empty varargin, pass the Null variant, which is converted to an empty MATLAB cell array when passed.

Example: Passing an Empty varargin from VBA Code

The following example illustrates how to pass the null variant in order to pass an empty varargin:

Function foo(x1 As Variant, x2 As Variant, x3 As Variant, _ 
             x4 As Variant, x5 As Variant) As Variant 
   Dim aClass As Object 
   Dim v(1 To 5) As Variant 
   Dim y As Variant 
    
   On Error Goto Handle_Error 
   v(1) = x1 
   v(2) = x2 
   v(3) = x3 
   v(4) = x4 
   v(5) = x5 
   aClass = CreateObject("mycomponent.myclass.1_0") 

   'Call aClass.foo(1,y,v) 
   Call aClass.foo(1,y,Null) 

   foo = y 
   Exit Function 
Handle_Error: 
   foo = Err.Description 
End Function

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Calling the Methods of a Class Instance

Calling Compiled MATLAB Functions from Microsoft Excel

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