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Data Conversion

Conversion Rules

This section describes the data conversion rules for COM components created with the MATLAB® Compiler SDK™ product. These components are dual interface COM objects that support data types compatible with Automation.

Note

Automation (formerly called OLE Automation) is a technology that allows software packages to expose their unique features to scripting tools and other applications. Automation uses the Component Object Model (COM), but may be implemented independently from other OLE features, such as in-place activation.

Caution

Be aware that IIS (Internet Information Service) usually prevents most COM automation on the basis that it may pose a security risk. Therefore, XLSREAD and other Automation services may fail when served by IIS, leading to errors such as object reference not set.

When a method is invoked on a MATLAB Compiler SDK component, the input parameters are converted to MATLAB internal array format and passed to the compiled MATLAB function. When the function exits, the output parameters are converted from MATLAB internal array format to COM Automation types.

The COM client passes all input and output arguments in the compiled MATLAB functions as type VARIANT. The COM VARIANT type is a union of several simple data types. A type VARIANT variable can store a variable of any of the simple types, as well as arrays of any of these values.

The Win32 API provides many functions for creating and manipulating VARIANTs in C/C++, and Microsoft® Visual Basic® provides native language support for this type. See the Microsoft Visual Studio® documentation for definitions and API support for COM VARIANTs. VARIANT variables are self describing and store their type code as an internal field of the structure.

Note

This discussion of data refers to both VARIANT and Variant data types. VARIANT is the C++ name and Variant is the corresponding data type in Visual Basic.

See VARIANT Type Codes Supported for a list of the VARIANT type codes supported by compiler components.

See MATLAB to COM VARIANT Conversion Rules and COM VARIANT to MATLAB Conversion Rules for conversion rules between COM VARIANTs and MATLAB arrays.

VARIANT Type Codes Supported

VARIANT Type Code
(C/C++)
C/C++ TypeVariant Type Code (Visual Basic)Visual Basic TypeDefinition
VT_EMPTY-vbEmpty-

Uninitialized VARIANT

VT_I1char--

Signed one-byte character

VT_UI1

unsigned char

vbByteByte

Unsigned one-byte character

VT_I2shortvbIntegerInteger

Signed two-byte integer

VT_UI2unsigned short--

Unsigned two-byte integer

VT_I4longvbLongLong

Signed four-byte integer

VT_UI4unsigned long--

Unsigned four-byte integer

VT_R4floatvbSingleSingle

IEEE® four-byte floating-point value

VT_R8doublevbDoubleDouble

IEEE eight-byte floating-point value

VT_CYCY+vbCurrencyCurrency

Currency value (64-bit integer, scaled by 10,000)

VT_BSTRBSTR+vbStringString

String value

VT_ERRORSCODE+vbError-

HRESULT (signed four-byte integer representing a COM error code)

VT_DATEDATE+vbDateDate

Eight-byte floating-point value representing date and time

VT_INTint--

Signed integer; equivalent to type int

VT_UINTunsigned int--

Unsigned integer; equivalent to type unsigned int

VT_DECIMALDECIMAL+vbDecimal-

96-bit (12-byte) unsigned integer, scaled by a variable power of 10

VT_BOOLVARIANT_BOOL+vbBooleanBoolean

Two-byte Boolean value (0xFFFF = True; 0x0000 = False)

VT_DISPATCHIDispatch*vbObjectObject

IDispatch* pointer to an object

VT_VARIANTVARIANT+vbVariantVariant

VARIANT (can only be specified if combined with VT_BYREF or VT_ARRAY)

<anything>|VT_ARRAY   

Bitwise combine VT_ARRAY with any basic type to declare as an array

<anything>|VT_BYREF   

Bitwise combine VT_BYREF with any basic type to declare as a reference to a value

+ Denotes Windows® specific type. Not part of standard C/C++.

MATLAB to COM VARIANT Conversion Rules

MATLAB Data TypeVARIANT Type for Scalar DataVARIANT Type for Array DataComments
cell

A 1-by-1 cell array converts to a single VARIANT with a type conforming to the conversion rule for the MATLAB data type of the cell contents.

A multidimensional cell array converts to a VARIANT of type VT_VARIANT|VT_ARRAY with the type of each array member conforming to the conversion rule for the MATLAB data type of the corresponding cell.

structure

VT_DISPATCH

VT_DISPATCH

A MATLAB struct array is converted to an MWStruct object. (See Class MWStruct.) This object is passed as a VT_DISPATCH type.

char

A 1-by-1 char matrix converts to a VARIANT of type VT_BSTR with string length = 1.

A 1-by-L char matrix is assumed to represent a string of length L in MATLAB. This case converts to a VARIANT of type VT_BSTR with a string length = L. char matrices of more than one row, or of a higher dimensionality convert to a VARIANT of type VT_BSTR|VT_ARRAY. Each string in the converted array is of length 1 and corresponds to each character in the original matrix.

Arrays of strings are not supported as char matrices. To pass an array of strings, use a cell array of 1-by-L char matrices.

sparse

VT_DISPATCH

VT_DISPATCH

A MATLAB sparse array is converted to an MWSparse object. (See Class MWSparse.) This object is passed as a VT_DISPATCH type.

double

A real 1-by-1 double matrix converts to a VARIANT of type VT_R8. A complex 1-by-1 double matrix converts to a VARIANT of type VT_DISPATCH.

A real multidimensional double matrix converts to a VARIANT of type VT_R8|VT_ARRAY.
A complex multidimensional double matrix converts to a VARIANT of type VT_DISPATCH.

Complex arrays are passed to and from compiled MATLAB functions using the MWComplex class. See Class MWComplex

single

A real 1-by-1 single matrix converts to a VARIANT of type VT_R4. A complex 1-by-1 single matrix converts to a VARIANT of type VT_DISPATCH.

A real multidimensional single matrix converts to a VARIANT of type VT_R4|VT_ARRAY.
A complex multidimensional single matrix converts to a VARIANT of type VT_DISPATCH.

Complex arrays are passed to and from compiled MATLAB functions using the MWComplex class.

int8

A real 1-by-1 int8 matrix converts to a VARIANT of type VT_I1. A complex 1-by-1 int8 matrix converts to a VARIANT of type VT_DISPATCH.

A real multidimensional int8 matrix converts to a VARIANT of type VT_I1|VT_ARRAY.
A complex multidimensional int8 matrix converts to a VARIANT of type VT_DISPATCH.

Complex arrays are passed to and from compiled MATLAB functions using the MWComplex class.

uint8

A real 1-by-1 uint8 matrix converts to a VARIANT of type VT_UI1. A complex 1-by-1 uint8 matrix converts to a VARIANT of type VT_DISPATCH.

A real multidimensional uint8 matrix converts to a VARIANT of type VT_UI1|VT_ARRAY.A complex multidimensional uint8 matrix converts to a VARIANT of type VT_DISPATCH.

Complex arrays are passed to and from compiled MATLAB functions using the MWComplex class.

int16

A real 1-by-1 int16 matrix converts to a VARIANT of type VT_I2. A complex 1-by-1 int16 matrix converts to a VARIANT of type VT_DISPATCH.

A real multidimensional int16 matrix converts to a VARIANT of type VT_I2|VT_ARRAY. A complex multidimensional int16 matrix converts to a VARIANT of type VT_DISPATCH.

Complex arrays are passed to and from compiled MATLAB functions using the MWComplex class.

uint16

A real 1-by-1 uint16 matrix converts to a VARIANT of type VT_UI2. A complex 1-by-1 uint16 matrix converts to a VARIANT of type VT_DISPATCH.

A real multidimensional uint16 matrix converts to a VARIANT of type VT_UI2|VT_ARRAY. A complex multidimensional uint16 matrix converts to a VARIANT of type VT_DISPATCH.

Complex arrays are passed to and from compiled MATLAB functions using the MWComplex class.

int32

A 1-by-1 int32 matrix converts to a VARIANT of type VT_I4. A complex 1-by-1 int32 matrix converts to a VARIANT of type VT_DISPATCH.

A multidimensional int32 matrix converts to a VARIANT of type VT_I4|VT_ARRAY. A complex multidimensional int32 matrix converts to a VARIANT of type VT_DISPATCH.

Complex arrays are passed to and from compiled MATLAB functions using the MWComplex class.

uint32

A 1-by-1 uint32 matrix converts to a VARIANT of type VT_UI4. A complex 1-by-1 uint32 matrix converts to a VARIANT of type VT_DISPATCH.

A multidimensional uint32 matrix converts to a VARIANT of type VT_UI4|VT_ARRAY. A complex multidimensional uint32 matrix converts to a VARIANT of type VT_DISPATCH.

Complex arrays are passed to and from compiled MATLAB functions using the MWComplex class.

Function handle

VT_EMPTY

VT_EMPTY

Not supported

Java® class

VT_EMPTY

VT_EMPTY

Not supported

User class

VT_EMPTY

VT_EMPTY

Not supported

logical

VT_Bool

VT_Bool|VT_ARRAY

COM VARIANT to MATLAB Conversion Rules

VARIANT TypeMATLAB Data Type (Scalar or Array Data)Comments
VT_EMPTY

N/A

Empty array created.

VT_I1int8

VT_UI1uint8

VT_I2int16

VT_UI2uint16

VT_I4int32

VT_UI4uint32

VT_R4single

VT_R8double

VT_CYdouble

VT_BSTRchar

A VARIANT of type VT_BSTR converts to a 1-by-L MATLAB char array, where L = the length of the string to be converted. A VARIANT of type VT_BSTR|VT_ARRAY converts to a MATLAB cell array of 1-by-L char arrays.

VT_ERRORint32

VT_DATEdouble

VARIANT dates are stored as doubles starting at midnight Dec. 31, 1899. MATLAB dates are stored as doubles starting at 0/0/00 00:00:00. Therefore, a VARIANT date of 0.0 maps to a MATLAB numeric date of 693960.0. VARIANT dates are converted to MATLAB double types and incremented by 693960.0.

VARIANT dates can be optionally converted to strings. See Data Conversion Flags for more information on type coercion.

VT_INTint32

VT_UINTuint32

VT_DECIMALdouble

VT_BOOLlogical

VT_DISPATCHVaries

IDispatch* pointers are treated within the context of what they point to. Objects must be supported types with known data extraction and conversion rules, or expose a generic Value property that points to a single VARIANT type. Data extracted from an object is converted based on the rules for the particular VARIANT obtained.

Currently, support exists for Excel® Range objects as well as the types MWStruct, MWComplex, MWSparse, and MWArg. See Reference Utility Classes for information on the types to use with COM components.

anything|VT_BYREFVaries

Pointers to any of the basic types are processed according to the rules for what they point to. The resulting MATLAB array contains a deep copy of the values.

anything|VT_ARRAYVaries

Multidimensional VARIANT arrays convert to multidimensional MATLAB arrays, each element converted according to the rules for the basic types. Multidimensional VARIANT arrays of type VT_VARIANT|VT_ARRAY convert to multidimensional cell arrays, each cell converted according to the rules for that specific type.

Array Formatting Flags

The components have flags that control how array data is formatted in both directions. Generally, you should develop client code that matches the intended inputs and outputs of the MATLAB functions with the corresponding methods on the compiled COM objects, in accordance with the rules listed in MATLAB to COM VARIANT Conversion Rules and COM VARIANT to MATLAB Conversion Rules. In some cases this is not possible, for example, when existing MATLAB code is used in conjunction with a third-party product like Excel.

The following table shows the array formatting flags.

Array Formatting Flags

Flag Description

InputArrayFormat

Defines the array formatting rule used on input arrays.
An input array is a VARIANT array, created by the client, sent as an input parameter to a method call on a compiled COM object.

Valid values for this flag are mwArrayFormatAsIs, mwArrayFormatMatrix, and mwArrayFormatCell.

mwArrayFormatAsIs passes the array unchanged.

mwArrayFormatMatrix (default) formats all arrays as matrices. When the input VARIANT is of type VT_ARRAY| type, where type is any numeric type, this flag has no effect. When the input VARIANT is of type VT_VARIANT|VT_ARRAY, VARIANTs in the array are examined. If they are single-valued and homogeneous in type, a MATLAB matrix of the appropriate type is produced instead of a cell array.

mwArrayFormatCell interprets all arrays as MATLAB cell arrays.

InputArrayIndFlag

Sets the input array indirection level used with the InputArrayFormat flag (applicable only to nested arrays, i.e., VARIANT arrays of VARIANTs, which themselves are arrays). The default value for this flag is zero, which applies the InputArrayFormat flag to the outermost array. When this flag is greater than zero, e.g., equal to N, the formatting rule attempts to apply itself to the Nth level of nesting.

OutputArrayFormat

Defines the array formatting rule used on output arrays. An output array is a MATLAB array, created by the compiled COM object, sent as an output parameter from a method call to the client. The values for this flag, mwArrayFormatAsIs, mwArrayFormatMatrix, and mwArrayFormatCell, cause the same behavior as the corresponding InputArrayFormat flag values.

OutputArrayIndFlag

(Applies to nested cell arrays only.) Output array indirection level used with the OutputArrayFormat flag. This flag works exactly like InputArrayIndFlag.

AutoResizeOutput

(Applies to Excel ranges only.) When the target output from a method call is a range of cells in an Excel worksheet and the output array size and shape is not known at the time of the call, set this flag to True to resize each Excel range to fit the output array.

TransposeOutput

Set this flag to True to transpose the output arguments. Useful when calling a component from Excel where the MATLAB function returns outputs as row vectors, and you want the data in columns.

Data Conversion Flags

MATLAB Compiler SDK components contain flags to control the conversion of certain VARIANT types to MATLAB types. These flags are as follows:

CoerceNumericToType

This flag tells the data converter to convert all numeric VARIANT data to one specific MATLAB type. VARIANT type codes affected by this flag are VT_I1, VT_UI1, VT_I2, VT_UI2, VT_I4, VT_UI4, VT_R4, VT_R8, VT_CY, VT_DECIMAL, VT_INT, VT_UINT, VT_ERROR, VT_BOOL, and VT_DATE. Valid values for this flag are mwTypeDefault, mwTypeChar, mwTypeDouble, mwTypeSingle, mwTypeLogical, mwTypeInt8, mwTypeUint8, mwTypeInt16, mwTypeUint16, mwTypeInt32, and mwTypeUint32.

The default for this flag, mwTypeDefault, converts numeric data according to the rules listed in Data Conversion.

InputDateFormat

This flag tells the data converter how to convert VARIANT dates to MATLAB dates. Valid values for this flag are mwDateFormatNumeric (default) and mwDateFormatString. The default converts VARIANT dates according to the rule listed in VARIANT Type Codes Supported . The mwDateFormatString flag converts a VARIANT date to its string representation. This flag only affects VARIANT type code VT_DATE.

OutputAsDate As Boolean

This flag instructs the data converter to process an output argument as a date. By default, numeric dates that are output parameters from compiled MATLAB functions are passed as Doubles that need to be decremented by the COM date bias (693960) as well as coerced to COM dates. Set this flag to True to convert all output values of type Double.

DateBias As Long

This flag sets the date bias for performing COM to MATLAB numeric date conversions. The default value of this property is 693960, which represents the difference between the COM Date type and MATLAB numeric dates. This flag allows existing MATLAB code that already performs the increment of numeric dates by 693960 to be used unchanged with the components. To process dates with such code, set this property to 0.

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