MATLAB: How to find out to which VARIANT type a MATLAB variable is converted

mapMATLABvariantargvtvt_boolvt_byrefvt_cyvt_datevt_decimalvt_dispatchvt_emptyvt_intvt_nullvt_uintvt_unknownvt_variant

I have a COM object that expects a variable of type Variant(Optional). I would like to know how MATLAB data types are mapped to COM VARIANT types so that I can pass the correct data.

Best Answer

Most MATLAB data types are mapped to a certain VARIANT type. As of R2010a, there are some unsupported MATLAB types, but limitations are subject to change in newer releases.

The attached component can be used to find out how MATLAB data types are mapped to VARIANT types and to test for different behavior in different releases. Installation and requirement information is included in the ZIP file. The following example shows how to use the component:

 >> varTester = actxserver('VariantTester.Tester')
 varTester =
COM.VariantTester_Tester
 >> varTester.invoke
 TestVariant = string TestVariant(handle, Variant(Optional))
 >> varTester.TestVariant()
 ans =
 VT_ERROR (SCODE)
 >> varTester.TestVariant('Hello world')
 ans =
 VT_BSTR (BSTR)
 >> varTester.TestVariant(12345)
 ans =
 VT_R8 (DOUBLE)
 >> varTester.TestVariant([])
 ans =
 VT_ERROR (SCODE)
 >> varTester.TestVariant([123 456])
 ans =
 VT_ARRAY | VT_R8 (DOUBLE)
 >> varTester.TestVariant({'123' '456'})
 ans =
 VT_ARRAY | VT_VARIANT
 >> varTester.TestVariant(int8(123))
 ans =
 VT_I1 (CHAR)
 >> varTester.TestVariant(int16(123))
 ans =
 VT_I2 (SHORT)
 >> varTester.TestVariant(int32(123))
 ans =
 VT_I4 (LONG)

Related Solutions

MATLAB: How to rename a sheet in Excel using the COM interface in MATLAB

You can rename an Excel sheet using the "Name" property of a sheet object. For example the following renames the first sheet of an Excel file:

filename = 'C:\SomeExcelFile.xls';
% Open Excel Automation server
Excel = actxserver('Excel.Application');
% Make Excel visible
Excel.Visible=1;
% Open Excel file
Workbook = Excel.Workbooks.Open(filename);
% Get the list of sheets in the workbook
Sheets = Excel.ActiveWorkbook.Sheets;
% Rename the first sheet
Sheets.Item(1).Name = 'This is sheet 1';

The following code then saves the Workbook, quits Excel and removes the COM server:

% Save the file
Workbook.Save();
% Quit Excel, remove the COM server and delete the related objects
Excel.Quit();
Excel.delete();
clear Excel;
clear Workbook;
clear Sheets;

MATLAB: How to pass arguments in C++ to a function with a VARARGIN signature that has been compiled to a Generic COM Component using MATLAB Builder NE

When a MATLAB function with a formal parameter of type VARARGIN is compiled to a Generic COM Component, the corresponding formal parameter of the compiled component is of type VARIANT.

In order to pass the actual arguments, you can create a SAFEARRAY of VARIANTs containing the arguments of different types and then store it in a variable of type VARIANT that will be accepted and interpreted correctly by the component, as follows:

// Declare variables.
VARIANT in, * inArray;
// Create SAFEARRAY of VARIANTs.
int cEntries = 4;
SAFEARRAY* psa = SafeArrayCreateVector(VT_VARIANT, 0, cEntries);
// Lock the SAFEARRAY and get a pointer to the VARIANT elements.
SafeArrayAccessData(psa, (void **)&inArray);
// Populate the SAFEARRAY with the actual arguments.
// Set string value:
V_BSTR(&inArray[0]) = SysAllocString(L"String argument 1");
V_VT(&inArray[0]) = VT_BSTR;
// Set another string value in a different way:
inArray[1].bstrVal = SysAllocString(L"String argument 2");
inArray[1].vt = VT_BSTR;
// Set double value:
V_R8(&inArray[2]) = 1.2;
V_VT(&inArray[2]) = VT_R8;
// Set another double value in a different way:
inArray[3].dblVal = 1.3;
inArray[3].vt = VT_R8;
// Decrement SAFEARRAY lock.
SafeArrayUnaccessData(psa);
// Set VARIANT type and store SAFEARRAY in it.
// The following two lines are equivalent.
V_VT(∈) = VT_ARRAY | VT_VARIANT;
// in.vt = VT_ARRAY | VT_VARIANT; 
// The following three lines are equivalent.
V_ARRAY(∈) = psa;
//in.parray = psa;
//in.byref = psa;
// Call Generic COM Component and pass the variable "in".
// [...]
// Dispose off SAFEARRAY.
SafeArrayDestroy(psa);

For related information, please see:

SAFEARRAY Data Type

https://docs.microsoft.com/en-us/windows/win32/api/oaidl/ns-oaidl-safearray

VARIANT and VARIANTARG

https://docs.microsoft.com/en-us/windows/win32/api/oaidl/ns-oaidl-variant

Handling COM Data in MATLAB Software

https://www.mathworks.com/help/compiler_sdk/com.html

Best Answer

Related Solutions

MATLAB: How to rename a sheet in Excel using the COM interface in MATLAB

MATLAB: How to pass arguments in C++ to a function with a VARARGIN signature that has been compiled to a Generic COM Component using MATLAB Builder NE

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