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COleVariant Class

  • Bài viết

Encapsulates the VARIANT data type.

Syntax

class COleVariant : public tagVARIANT

Members

Public Constructors

Name Description
COleVariant::COleVariant Constructs a COleVariant object.

Public Methods

Name Description
COleVariant::Attach Attaches a VARIANT to a COleVariant.
COleVariant::ChangeType Changes the variant type of this COleVariant object.
COleVariant::Clear Clears this COleVariant object.
COleVariant::Detach Detaches a VARIANT from a COleVariant and returns the VARIANT.
COleVariant::GetByteArrayFromVariantArray Retrieves a byte array from an existing variant array.
COleVariant::SetString Sets the string to a particular type, typically ANSI.

Public Operators

Name Description
COleVariant::operator LPCVARIANT Converts a COleVariant value into an LPCVARIANT.
COleVariant::operator LPVARIANT Converts a COleVariant object into an LPVARIANT.
COleVariant::operator = Copies a COleVariant value.
COleVariant::operator == Compares two COleVariant values.
COleVariant::operator <<, COleVariant::operator >> Outputs a COleVariant value to CArchive or CDumpContext and inputs a COleVariant object from CArchive.

Remarks

This data type is used in OLE automation. Specifically, the DISPPARAMS structure contains a pointer to an array of VARIANT structures. A DISPPARAMS structure is used to pass parameters to IDispatch::Invoke.

Note

This class is derived from the VARIANT structure. This means you can pass a COleVariant in a parameter that calls for a VARIANT and that the data members of the VARIANT structure are accessible data members of COleVariant.

The two related MFC classes COleCurrency and COleDateTime encapsulate the variant data types CURRENCY ( VT_CY) and DATE ( VT_DATE). The COleVariant class is used extensively in the DAO classes; see these classes for typical usage of this class, for example CDaoQueryDef and CDaoRecordset.

For more information, see the VARIANT, CURRENCY, DISPPARAMS, and IDispatch::Invoke entries in the Windows SDK.

For more information on the COleVariant class and its use in OLE automation, see "Passing Parameters in OLE Automation" in the article Automation.

Inheritance Hierarchy

tagVARIANT

COleVariant

Requirements

Header: afxdisp.h

COleVariant::Attach

Call this function to attach the given VARIANT object to the current COleVariant object.

void Attach(VARIANT& varSrc);

Parameters

varSrc
An existing VARIANT object to be attached to the current COleVariant object.

Remarks

This function sets the VARTYPE of varSrc to VT_EMPTY.

For more information, see the VARIANT and VARENUM entries in the Windows SDK.

COleVariant::COleVariant

Constructs a COleVariant object.

COleVariant();
COleVariant(const VARIANT& varSrc);
COleVariant(const COleVariant& varSrc);
COleVariant(LPCVARIANT pSrc);
COleVariant(LPCTSTR lpszSrc);
COleVariant(LPCTSTR lpszSrc, VARTYPE vtSrc);
COleVariant(CString& strSrc);
COleVariant(BYTE nSrc);
COleVariant(short nSrc, VARTYPE vtSrc = VT_I2);
COleVariant(long lSrc,VARTYPE vtSrc = VT_I4);
COleVariant(const COleCurrency& curSrc);
COleVariant(float fltSrc);
COleVariant(double dblSrc);
COleVariant(const COleDateTime& timeSrc);
COleVariant(const CByteArray& arrSrc);
COleVariant(const CLongBinary& lbSrc);
COleVariant(LPCITEMIDLIST pidl);

Parameters

varSrc
An existing COleVariant or VARIANT object to be copied into the new COleVariant object.

pSrc
A pointer to a VARIANT object that will be copied into the new COleVariant object.

lpszSrc
A null-terminated string to be copied into the new COleVariant object.

vtSrc
The VARTYPE for the new COleVariant object.

strSrc
A CString object to be copied into the new COleVariant object.

nSrc, lSrc A numerical value to be copied into the new COleVariant object.

vtSrc
The VARTYPE for the new COleVariant object.

curSrc
A COleCurrency object to be copied into the new COleVariant object.

fltSrc, dblSrc
A numerical value to be copied into the new COleVariant object.

timeSrc
A COleDateTime object to be copied into the new COleVariant object.

arrSrc
A CByteArray object to be copied into the new COleVariant object.

lbSrc
A CLongBinary object to be copied into the new COleVariant object.

pidl
A pointer to an ITEMIDLIST structure to be copied into the new COleVariant object.

Remarks

All these constructors create new COleVariant objects initialized to the specified value. A brief description of each of these constructors follows.

  • COleVariant( ) Creates an empty COleVariant object, VT_EMPTY.

  • COleVariant( varSrc ) Copies an existing VARIANT or COleVariant object. The variant type is retained.

  • COleVariant( pSrc ) Copies an existing VARIANT or COleVariant object. The variant type is retained.

  • COleVariant( lpszSrc ) Copies a string into the new object, VT_BSTR (UNICODE).

  • COleVariant( lpszSrc , vtSrc ) Copies a string into the new object. The parameter vtSrc must be VT_BSTR (UNICODE) or VT_BSTRT (ANSI).

  • COleVariant( strSrc ) Copies a string into the new object, VT_BSTR (UNICODE).

  • COleVariant( nSrc ) Copies an 8-bit integer into the new object, VT_UI1.

  • COleVariant( nSrc , vtSrc ) Copies a 16-bit integer (or Boolean value) into the new object. The parameter vtSrc must be VT_I2 or VT_BOOL.

  • COleVariant( lSrc , vtSrc ) Copies a 32-bit integer (or SCODE value) into the new object. The parameter vtSrc must be VT_I4, VT_ERROR, or VT_BOOL.

  • COleVariant( curSrc ) Copies a COleCurrency value into the new object, VT_CY.

  • COleVariant( fltSrc ) Copies a 32-bit floating-point value into the new object, VT_R4.

  • COleVariant( dblSrc ) Copies a 64-bit floating-point value into the new object, VT_R8.

  • COleVariant( timeSrc ) Copies a COleDateTime value into the new object, VT_DATE.

  • COleVariant( arrSrc ) Copies a CByteArray object into the new object, VT_EMPTY.

  • COleVariant( lbSrc ) Copies a CLongBinary object into the new object, VT_EMPTY.

For more information on SCODE, see Structure of COM Error Codes in the Windows SDK.

COleVariant::ChangeType

Converts the type of variant value in this COleVariant object.

void ChangeType(VARTYPE vartype, LPVARIANT pSrc = NULL);

Parameters

vartype
The VARTYPE for this COleVariant object.

pSrc
A pointer to the VARIANT object to be converted. If this value is NULL, this COleVariant object is used as the source for the conversion.

Remarks

For more information, see the VARIANT, VARENUM, and VariantChangeType entries in the Windows SDK.

COleVariant::Clear

Clears the VARIANT.

void Clear();

Remarks

This sets the VARTYPE for this object to VT_EMPTY. The COleVariant destructor calls this function.

For more information, see the VARIANT, VARTYPE, and VariantClear entries in the Windows SDK.

COleVariant::Detach

Detaches the underlying VARIANT object from this COleVariant object.

VARIANT Detach();

Remarks

This function sets the VARTYPE for this COleVariant object to VT_EMPTY.

Note

After calling Detach, it is the caller's responsibility to call VariantClear on the resulting VARIANT structure.

For more information, see the VARIANT, VARENUM, and VariantClear entries in the Windows SDK.

COleVariant::GetByteArrayFromVariantArray

Retrieves a byte array from an existing variant array

void GetByteArrayFromVariantArray(CByteArray& bytes);

Parameters

bytes
A reference to an existing CByteArray object.

COleVariant::operator LPCVARIANT

This casting operator returns a VARIANT structure whose value is copied from this COleVariant object.

operator LPCVARIANT() const;

Remarks

COleVariant::operator LPVARIANT

Call this casting operator to access the underlying VARIANT structure for this COleVariant object.

operator LPVARIANT();

Remarks

Caution

Changing the value in the VARIANT structure accessed by the pointer returned by this function will change the value of this COleVariant object.

COleVariant::operator =

These overloaded assignment operators copy the source value into this COleVariant object.

const COleVariant& operator=(const VARIANT& varSrc);
const COleVariant& operator=(LPCVARIANT pSrc);
const COleVariant& operator=(const COleVariant& varSrc);
const COleVariant& operator=(const LPCTSTR lpszSrc);
const COleVariant& operator=(const CString& strSrc);
const COleVariant& operator=(BYTE nSrc);
const COleVariant& operator=(short nSrc);
const COleVariant& operator=(long lSrc);
const COleVariant& operator=(const COleCurrency& curSrc);
const COleVariant& operator=(float fltSrc);
const COleVariant& operator=(double dblSrc);
const COleVariant& operator=(const COleDateTime& dateSrc);
const COleVariant& operator=(const CByteArray& arrSrc);
const COleVariant& operator=(const CLongBinary& lbSrc);

Remarks

A brief description of each operator follows:

  • operator =( varSrc ) Copies an existing VARIANT or COleVariant object into this object.

  • operator =( pSrc ) Copies the VARIANT object accessed by pSrc into this object.

  • operator =( lpszSrc ) Copies a null-terminated string into this object and sets the VARTYPE to VT_BSTR.

  • operator =( strSrc ) Copies a CString object into this object and sets the VARTYPE to VT_BSTR.

  • operator =( nSrc ) Copies an 8- or 16-bit integer value into this object. If nSrc is an 8-bit value, the VARTYPE of this is set to VT_UI1. If nSrc is a 16-bit value and the VARTYPE of this is VT_BOOL, it is kept; otherwise, it is set to VT_I2.

  • operator =( lSrc ) Copies a 32-bit integer value into this object. If the VARTYPE of this is VT_ERROR, it is kept; otherwise, it is set to VT_I4.

  • operator =( curSrc ) Copies a COleCurrency object into this object and sets the VARTYPE to VT_CY.

  • operator =( fltSrc ) Copies a 32-bit floating-point value into this object and sets the VARTYPE to VT_R4.

  • operator =( dblSrc ) Copies a 64-bit floating-point value into this object and sets the VARTYPE to VT_R8.

  • operator =( dateSrc ) Copies a COleDateTime object into this object and sets the VARTYPE to VT_DATE.

  • operator =( arrSrc ) Copies a CByteArray object into this COleVariant object.

  • operator =( lbSrc ) Copies a CLongBinary object into this COleVariant object.

For more information, see the VARIANT and VARENUM entries in the Windows SDK.

COleVariant::operator ==

This operator compares two variant values and returns nonzero if they are equal; otherwise 0.

BOOL operator==(const VARIANT& varSrc) const;
BOOL operator==(LPCVARIANT pSrc) const;

COleVariant::operator <<, COleVariant::operator >>

Outputs a COleVariant value to CArchive or CdumpContext and inputs a COleVariant object from CArchive.

friend CDumpContext& AFXAPI operator<<(
    CDumpContext& dc,
    OleVariant varSrc);

friend CArchive& AFXAPI operator<<(
    CArchive& ar,
    COleVariant varSrc);

friend CArchive& AFXAPI operator>>(
    CArchive& ar,
    COleVariant& varSrc);

Remarks

The COleVariant insertion (<<) operator supports diagnostic dumping and storing to an archive. The extraction (>>) operator supports loading from an archive.

COleVariant::SetString

Sets the string to a particular type.

void SetString(LPCTSTR lpszSrc, VARTYPE vtSrc);

Parameters

lpszSrc
A null-terminated string to be copied into the new COleVariant object.

VtSrc
The VARTYPE for the new COleVariant object.

Remarks

The parameter vtSrc must be VT_BSTR (UNICODE) or VT_BSTRT (ANSI). SetString is typically used to set strings to ANSI, since the default for the COleVariant::COleVariant constructor with a string or string pointer parameter and no VARTYPE is UNICODE.

A DAO recordset in a non-UNICODE build expects strings to be ANSI. Thus, for DAO functions that use COleVariant objects, if you are not creating a UNICODE recordset, you must use the COleVariant::COleVariant( lpszSrc , vtSrc ) form of constructor with vtSrc set to VT_BSTRT (ANSI) or use SetString with vtSrc set to VT_BSTRT to make ANSI strings. For example, the CDaoRecordset functions CDaoRecordset::Seek and CDaoRecordset::SetFieldValue use COleVariant objects as parameters. These objects must be ANSI if the DAO recordset is not UNICODE.

See also

Hierarchy Chart