QVariant  是一个变体数据类型类 ，封装了类似c++ VARIANT  这种结构体的数据类型！

QVariant 这个类型充当着最常见的数据类型的联合。QVariant 可以保存很多Qt的数据类型，包括QBrush、QColor、QCursor、QDateTime、QFont、QKeySequence、 QPalette、QPen、QPixmap、QPoint、QRect、QRegion、QSize和QString，并且还有C++基本类型，如 int、float等。

当然，如果支持的类型没有想要的，没关系，QVariant也可以支持自定义的数据类型。被QVariant存储的数据类型需要有一个默认的构造函数和一个拷贝构造函数。为了实现这个功能，首先必须使用Q_DECLARE_METATYPE()宏。通常会将这个宏放在类的声明所在头文件的下面：

Q_DECLARE_METATYPE(MyClass)

class Q_CORE_EXPORT QVariant
{
 public:
    enum Type {
        Invalid = QMetaType::UnknownType,
        Bool = QMetaType::Bool,
        Int = QMetaType::Int,
        UInt = QMetaType::UInt,
        LongLong = QMetaType::LongLong,
        ULongLong = QMetaType::ULongLong,
        Double = QMetaType::Double,
        Char = QMetaType::QChar,
        Map = QMetaType::QVariantMap,
        List = QMetaType::QVariantList,
        String = QMetaType::QString,
        StringList = QMetaType::QStringList,
        ByteArray = QMetaType::QByteArray,
        BitArray = QMetaType::QBitArray,
        Date = QMetaType::QDate,
        Time = QMetaType::QTime,
        DateTime = QMetaType::QDateTime,
        Url = QMetaType::QUrl,
        Locale = QMetaType::QLocale,
        Rect = QMetaType::QRect,
        RectF = QMetaType::QRectF,
        Size = QMetaType::QSize,
        SizeF = QMetaType::QSizeF,
        Line = QMetaType::QLine,
        LineF = QMetaType::QLineF,
        Point = QMetaType::QPoint,
        PointF = QMetaType::QPointF,
        RegExp = QMetaType::QRegExp,
        RegularExpression = QMetaType::QRegularExpression,
        Hash = QMetaType::QVariantHash,
        EasingCurve = QMetaType::QEasingCurve,
        Uuid = QMetaType::QUuid,
#if QT_CONFIG(itemmodel)
        ModelIndex = QMetaType::QModelIndex,
        PersistentModelIndex = QMetaType::QPersistentModelIndex,
#endif
        LastCoreType = QMetaType::LastCoreType,

        Font = QMetaType::QFont,
        Pixmap = QMetaType::QPixmap,
        Brush = QMetaType::QBrush,
        Color = QMetaType::QColor,
        Palette = QMetaType::QPalette,
        Image = QMetaType::QImage,
        Polygon = QMetaType::QPolygon,
        Region = QMetaType::QRegion,
        Bitmap = QMetaType::QBitmap,
        Cursor = QMetaType::QCursor,
        KeySequence = QMetaType::QKeySequence,
        Pen = QMetaType::QPen,
        TextLength = QMetaType::QTextLength,
        TextFormat = QMetaType::QTextFormat,
        Matrix = QMetaType::QMatrix,
        Transform = QMetaType::QTransform,
        Matrix4x4 = QMetaType::QMatrix4x4,
        Vector2D = QMetaType::QVector2D,
        Vector3D = QMetaType::QVector3D,
        Vector4D = QMetaType::QVector4D,
        Quaternion = QMetaType::QQuaternion,
        PolygonF = QMetaType::QPolygonF,
        Icon = QMetaType::QIcon,
        LastGuiType = QMetaType::LastGuiType,

        SizePolicy = QMetaType::QSizePolicy,

        UserType = QMetaType::User,
        LastType = 0xffffffff // need this so that gcc >= 3.4 allocates 32 bits for Type
    };

    QVariant() Q_DECL_NOTHROW : d() {}
    ~QVariant();
    QVariant(Type type);
    QVariant(int typeId, const void *copy);
    QVariant(int typeId, const void *copy, uint flags);
    QVariant(const QVariant &other);

#ifndef QT_NO_DATASTREAM
    QVariant(QDataStream &s);
#endif

    QVariant(int i);
    QVariant(uint ui);
    QVariant(qlonglong ll);
    QVariant(qulonglong ull);
    QVariant(bool b);
    QVariant(double d);
    QVariant(float f);
#ifndef QT_NO_CAST_FROM_ASCII
    QT_ASCII_CAST_WARN QVariant(const char *str);
#endif

    QVariant(const QByteArray &bytearray);
    QVariant(const QBitArray &bitarray);
    QVariant(const QString &string);
    QVariant(QLatin1String string);
    QVariant(const QStringList &stringlist);
    QVariant(QChar qchar);
    QVariant(const QDate &date);
    QVariant(const QTime &time);
    QVariant(const QDateTime &datetime);
    QVariant(const QList<QVariant> &list);
    QVariant(const QMap<QString,QVariant> &map);
    QVariant(const QHash<QString,QVariant> &hash);
#ifndef QT_NO_GEOM_VARIANT
    QVariant(const QSize &size);
    QVariant(const QSizeF &size);
    QVariant(const QPoint &pt);
    QVariant(const QPointF &pt);
    QVariant(const QLine &line);
    QVariant(const QLineF &line);
    QVariant(const QRect &rect);
    QVariant(const QRectF &rect);
#endif
    QVariant(const QLocale &locale);
#ifndef QT_NO_REGEXP
    QVariant(const QRegExp &regExp);
#endif // QT_NO_REGEXP
#if QT_CONFIG(regularexpression)
    QVariant(const QRegularExpression &re);
#endif // QT_CONFIG(regularexpression)
#ifndef QT_BOOTSTRAPPED
    QVariant(const QUrl &url);
    QVariant(const QEasingCurve &easing);
    QVariant(const QUuid &uuid);
    QVariant(const QJsonValue &jsonValue);
    QVariant(const QJsonObject &jsonObject);
    QVariant(const QJsonArray &jsonArray);
    QVariant(const QJsonDocument &jsonDocument);
#endif // QT_BOOTSTRAPPED
#if QT_CONFIG(itemmodel)
    QVariant(const QModelIndex &modelIndex);
    QVariant(const QPersistentModelIndex &modelIndex);
#endif

    QVariant& operator=(const QVariant &other);
#ifdef Q_COMPILER_RVALUE_REFS
    inline QVariant(QVariant &&other) Q_DECL_NOTHROW : d(other.d)
    { other.d = Private(); }
    inline QVariant &operator=(QVariant &&other) Q_DECL_NOTHROW
    { qSwap(d, other.d); return *this; }
#endif

    inline void swap(QVariant &other) Q_DECL_NOTHROW { qSwap(d, other.d); }

    Type type() const;
    int userType() const;
    const char *typeName() const;

    bool canConvert(int targetTypeId) const;
    bool convert(int targetTypeId);

    inline bool isValid() const;
    bool isNull() const;

    void clear();

    void detach();
    inline bool isDetached() const;

    int toInt(bool *ok = nullptr) const;
    uint toUInt(bool *ok = nullptr) const;
    qlonglong toLongLong(bool *ok = nullptr) const;
    qulonglong toULongLong(bool *ok = nullptr) const;
    bool toBool() const;
    double toDouble(bool *ok = nullptr) const;
    float toFloat(bool *ok = nullptr) const;
    qreal toReal(bool *ok = nullptr) const;
    QByteArray toByteArray() const;
    QBitArray toBitArray() const;
    QString toString() const;
    QStringList toStringList() const;
    QChar toChar() const;
    QDate toDate() const;
    QTime toTime() const;
    QDateTime toDateTime() const;
    QList<QVariant> toList() const;
    QMap<QString, QVariant> toMap() const;
    QHash<QString, QVariant> toHash() const;

#ifndef QT_NO_GEOM_VARIANT
    QPoint toPoint() const;
    QPointF toPointF() const;
    QRect toRect() const;
    QSize toSize() const;
    QSizeF toSizeF() const;
    QLine toLine() const;
    QLineF toLineF() const;
    QRectF toRectF() const;
#endif
    QLocale toLocale() const;
#ifndef QT_NO_REGEXP
    QRegExp toRegExp() const;
#endif // QT_NO_REGEXP
#if QT_CONFIG(regularexpression)
    QRegularExpression toRegularExpression() const;
#endif // QT_CONFIG(regularexpression)
#ifndef QT_BOOTSTRAPPED
    QUrl toUrl() const;
    QEasingCurve toEasingCurve() const;
    QUuid toUuid() const;
    QJsonValue toJsonValue() const;
    QJsonObject toJsonObject() const;
    QJsonArray toJsonArray() const;
    QJsonDocument toJsonDocument() const;
#endif // QT_BOOTSTRAPPED
#if QT_CONFIG(itemmodel)
    QModelIndex toModelIndex() const;
    QPersistentModelIndex toPersistentModelIndex() const;
#endif

#ifndef QT_NO_DATASTREAM
    void load(QDataStream &ds);
    void save(QDataStream &ds) const;
#endif
    static const char *typeToName(int typeId);
    static Type nameToType(const char *name);

    void *data();
    const void *constData() const;
    inline const void *data() const { return constData(); }

    template<typename T>
    inline void setValue(const T &value);

    template<typename T>
    inline T value() const
    { return qvariant_cast<T>(*this); }

    template<typename T>
    static inline QVariant fromValue(const T &value)
    { return qVariantFromValue(value); }

#if QT_HAS_INCLUDE(<variant>) && __cplusplus >= 201703L
    template<typename... Types>
    static inline QVariant fromStdVariant(const std::variant<Types...> &value)
    {
        if (value.valueless_by_exception())
            return QVariant();
        return std::visit([](const auto &arg) { return fromValue(arg); }, value);
    }
#endif

    template<typename T>
    bool canConvert() const
    { return canConvert(qMetaTypeId<T>()); }

 public:
    struct PrivateShared
    {
        inline PrivateShared(void *v) : ptr(v), ref(1) { }
        void *ptr;
        QAtomicInt ref;
    };
    struct Private
    {
        inline Private() Q_DECL_NOTHROW : type(Invalid), is_shared(false), is_null(true)
        { data.ptr = nullptr; }

        // Internal constructor for initialized variants.
        explicit inline Private(uint variantType) Q_DECL_NOTHROW
            : type(variantType), is_shared(false), is_null(false)
        {}

#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
        Private(const Private &other) Q_DECL_NOTHROW
            : data(other.data), type(other.type),
              is_shared(other.is_shared), is_null(other.is_null)
        {}
        Private &operator=(const Private &other) Q_DECL_NOTHROW = default;
#endif
        union Data
        {
            char c;
            uchar uc;
            short s;
            signed char sc;
            ushort us;
            int i;
            uint u;
            long l;
            ulong ul;
            bool b;
            double d;
            float f;
            qreal real;
            qlonglong ll;
            qulonglong ull;
            QObject *o;
            void *ptr;
            PrivateShared *shared;
        } data;
        uint type : 30;
        uint is_shared : 1;
        uint is_null : 1;
    };
 public:
    typedef void (*f_construct)(Private *, const void *);
    typedef void (*f_clear)(Private *);
    typedef bool (*f_null)(const Private *);
#ifndef QT_NO_DATASTREAM
    typedef void (*f_load)(Private *, QDataStream &);
    typedef void (*f_save)(const Private *, QDataStream &);
#endif
    typedef bool (*f_compare)(const Private *, const Private *);
    typedef bool (*f_convert)(const QVariant::Private *d, int t, void *, bool *);
    typedef bool (*f_canConvert)(const QVariant::Private *d, int t);
    typedef void (*f_debugStream)(QDebug, const QVariant &);
    struct Handler {
        f_construct construct;
        f_clear clear;
        f_null isNull;
#ifndef QT_NO_DATASTREAM
        f_load load;
        f_save save;
#endif
        f_compare compare;
        f_convert convert;
        f_canConvert canConvert;
        f_debugStream debugStream;
    };

    inline bool operator==(const QVariant &v) const
    { return cmp(v); }
    inline bool operator!=(const QVariant &v) const
    { return !cmp(v); }
    inline bool operator<(const QVariant &v) const
    { return compare(v) < 0; }
    inline bool operator<=(const QVariant &v) const
    { return compare(v) <= 0; }
    inline bool operator>(const QVariant &v) const
    { return compare(v) > 0; }
    inline bool operator>=(const QVariant &v) const
    { return compare(v) >= 0; }

protected:
    friend inline bool operator==(const QVariant &, const QVariantComparisonHelper &);
#ifndef QT_NO_DEBUG_STREAM
    friend Q_CORE_EXPORT QDebug operator<<(QDebug, const QVariant &);
#endif
// ### Qt6: FIXME: Remove the special Q_CC_MSVC handling, it was introduced to maintain BC for QTBUG-41810 .
#if !defined(Q_NO_TEMPLATE_FRIENDS) && !defined(Q_CC_MSVC)
    template<typename T>
    friend inline T qvariant_cast(const QVariant &);
    template<typename T> friend struct QtPrivate::QVariantValueHelper;
protected:
#else
public:
#endif
    Private d;
    void create(int type, const void *copy);
    bool cmp(const QVariant &other) const;
    int compare(const QVariant &other) const;
    bool convert(const int t, void *ptr) const; // ### Qt6: drop const

private:
    // force compile error, prevent QVariant(bool) to be called
    inline QVariant(void *) Q_DECL_EQ_DELETE;
    // QVariant::Type is marked as \obsolete, but we don't want to
    // provide a constructor from its intended replacement,
    // QMetaType::Type, instead, because the idea behind these
    // constructors is flawed in the first place. But we also don't
    // want QVariant(QMetaType::String) to compile and falsely be an
    // int variant, so delete this constructor:
    QVariant(QMetaType::Type) Q_DECL_EQ_DELETE;

    // These constructors don't create QVariants of the type associcated
    // with the enum, as expected, but they would create a QVariant of
    // type int with the value of the enum value.
    // Use QVariant v = QColor(Qt::red) instead of QVariant v = Qt::red for
    // example.
    QVariant(Qt::GlobalColor) Q_DECL_EQ_DELETE;
    QVariant(Qt::BrushStyle) Q_DECL_EQ_DELETE;
    QVariant(Qt::PenStyle) Q_DECL_EQ_DELETE;
    QVariant(Qt::CursorShape) Q_DECL_EQ_DELETE;
#ifdef QT_NO_CAST_FROM_ASCII
    // force compile error when implicit conversion is not wanted
    inline QVariant(const char *) Q_DECL_EQ_DELETe;
#endif
public:
    typedef Private DataPtr;
    inline DataPtr &data_ptr() { return d; }
    inline const DataPtr &data_ptr() const { return d; }
};

 excample:

  //普通使用
    QVariant var;
    var.setValue(12);
    int data=var.toInt();

自定义类型：

 struct ST_TYPE
{
    EN_RESULT_TYPE en_type;
    QString msg;
    ST_TYPE(EN_RESULT_TYPE _en_type, QString _msg) :en_type(_en_type), msg(_msg) {}
    ST_TYPE() {}
};
//注册自定义类型，待注册的自定义类型必须有不带参数的构造函数
Q_DECLARE_METATYPE(ST_TYPE)


//使用
    ST_TYPE st(EN_DEV_SN, QString(resultBuf));
    QVariant data;
    data.setValue(st);

指针用法：

        //保存
        QVariant var=QVariant::fromValue((void*)event);
        
        //获取
        QPaintEvent* e=(QPaintEvent*)var.value<void*>();

VARIANT：变体数据类型

typedef  struct tagVARIANT VARIANT;
struct tagVARIANT
    {
    union 
        {
        struct __tagVARIANT
            {
            VARTYPE vt;
            WORD wReserved1;
            WORD wReserved2;
            WORD wReserved3;
            union 
                {
                LONGLONG llVal;
                LONG lVal;
                BYTE bVal;
                SHORT iVal;
                FLOAT fltVal;
                DOUBLE dblVal;
                VARIANT_BOOL boolVal;
                _VARIANT_BOOL bool;
                SCODE scode;
                CY cyVal;
                DATE date;
                BSTR bstrVal;
                IUnknown *punkVal;
                IDispatch *pdispVal;
                SAFEARRAY *parray;
                BYTE *pbVal;
                SHORT *piVal;
                LONG *plVal;
                LONGLONG *pllVal;
                FLOAT *pfltVal;
                DOUBLE *pdblVal;
                VARIANT_BOOL *pboolVal;
                _VARIANT_BOOL *pbool;
                SCODE *pscode;
                CY *pcyVal;
                DATE *pdate;
                BSTR *pbstrVal;
                IUnknown **ppunkVal;
                IDispatch **ppdispVal;
                SAFEARRAY **pparray;
                VARIANT *pvarVal;
                PVOID byref;
                CHAR cVal;
                USHORT uiVal;
                ULONG ulVal;
                ULONGLONG ullVal;
                INT intVal;
                UINT uintVal;
                DECIMAL *pdecVal;
                CHAR *pcVal;
                USHORT *puiVal;
                ULONG *pulVal;
                ULONGLONG *pullVal;
                INT *pintVal;
                UINT *puintVal;
                struct __tagBRECORD
                    {
                    PVOID pvRecord;
                    IRecordInfo *pRecInfo;
                    } 	__VARIANT_NAME_4;
                } 	__VARIANT_NAME_3;
            } 	__VARIANT_NAME_2;
        DECIMAL decVal;
        } 	__VARIANT_NAME_1;
    } ;
typedef VARIANT *LPVARIANT;

typedef VARIANT VARIANTARG;

typedef VARIANT *LPVARIANTARG;

VARIANT数据结构包含两个域。vt域描述了第二个域的数据类型。为了使多种类型能够在第二个域中出现，我们定义了一个联合结构。所以，第二个域的名称随着vt域中输入值的不同而改变。用于指定vt域值情况的常量在联合的定义中以每一行的注释形式给出

int lValue = 888;  
VARIANT vParam;  
vParam.vt = VT_I4;  
vParam.lVal = lValue;


 vParam.vt = VT_BOOL;        //bool
 vParam.boolVal = true;
 cout<<vParam.boolVal<<endl;


  vParam.vt = VT_R8;        //double
  vParam.dblVal = 3.23;
  cout<<vParam.dblVal<<endl;

相关的 vt类型 定义如下

enum VARENUM
    {
        VT_EMPTY	= 0,
        VT_NULL	= 1,
        VT_I2	= 2,
        VT_I4	= 3,
        VT_R4	= 4,
        VT_R8	= 5,
        VT_CY	= 6,
        VT_DATE	= 7,
        VT_BSTR	= 8,
        VT_DISPATCH	= 9,
        VT_ERROR	= 10,
        VT_BOOL	= 11,
        VT_VARIANT	= 12,
        VT_UNKNOWN	= 13,
        VT_DECIMAL	= 14,
        VT_I1	= 16,
        VT_UI1	= 17,
        VT_UI2	= 18,
        VT_UI4	= 19,
        VT_I8	= 20,
        VT_UI8	= 21,
        VT_INT	= 22,
        VT_UINT	= 23,
        VT_VOID	= 24,
        VT_HRESULT	= 25,
        VT_PTR	= 26,
        VT_SAFEARRAY	= 27,
        VT_CARRAY	= 28,
        VT_USERDEFINED	= 29,
        VT_LPSTR	= 30,
        VT_LPWSTR	= 31,
        VT_RECORD	= 36,
        VT_INT_PTR	= 37,
        VT_UINT_PTR	= 38,
        VT_FILETIME	= 64,
        VT_BLOB	= 65,
        VT_STREAM	= 66,
        VT_STORAGE	= 67,
        VT_STREAMED_OBJECT	= 68,
        VT_STORED_OBJECT	= 69,
        VT_BLOB_OBJECT	= 70,
        VT_CF	= 71,
        VT_CLSID	= 72,
        VT_VERSIONED_STREAM	= 73,
        VT_BSTR_BLOB	= 0xfff,
        VT_VECTOR	= 0x1000,
        VT_ARRAY	= 0x2000,
        VT_BYREF	= 0x4000,
        VT_RESERVED	= 0x8000,
        VT_ILLEGAL	= 0xffff,
        VT_ILLEGALMASKED	= 0xfff,
        VT_TYPEMASK	= 0xfff
    } ;

主要分为两步：第一步是确定输入数据的类型，根据自己需要的类型在第一张vt域的值图中找到对应的值类型，初始化vt域值：

 vParam.vt  = xxxx; //对应的值类型，如int型就是VT_I4  要考虑32、64位

                         第二步就是根据第二张数据内容标识图根据之前vt域确定的数据类型找到成员对其进行赋值：

vParam.lVal = 100999; //int型对应的成员标识符为lVal，对var.lVal成员赋值100999

 _variant_t 类是对VARIANT的一个继承与封装，这就与  QVariant基本功能类似了

class _variant_t : public ::tagVARIANT {
public:
    // Constructors
    //
    _variant_t() throw();

    _variant_t(const VARIANT& varSrc) ;
    _variant_t(const VARIANT* pSrc) ;
    _variant_t(const _variant_t& varSrc) ;

    _variant_t(VARIANT& varSrc, bool fCopy) ;          // Attach VARIANT if !fCopy

    _variant_t(short sSrc, VARTYPE vtSrc = VT_I2) ;    // Creates a VT_I2, or a VT_BOOL
    _variant_t(long lSrc, VARTYPE vtSrc = VT_I4) ;     // Creates a VT_I4, a VT_ERROR, or a VT_BOOL
    _variant_t(float fltSrc) throw();                                   // Creates a VT_R4
    _variant_t(double dblSrc, VARTYPE vtSrc = VT_R8) ; // Creates a VT_R8, or a VT_DATE
    _variant_t(const CY& cySrc) throw();                                // Creates a VT_CY
    _variant_t(const _bstr_t& bstrSrc) ;               // Creates a VT_BSTR
    _variant_t(const wchar_t *pSrc) ;                  // Creates a VT_BSTR
    _variant_t(const char* pSrc) ;                     // Creates a VT_BSTR
    _variant_t(IDispatch* pSrc, bool fAddRef = true) throw();           // Creates a VT_DISPATCH
    _variant_t(bool boolSrc) throw();                                   // Creates a VT_BOOL
    _variant_t(IUnknown* pSrc, bool fAddRef = true) throw();            // Creates a VT_UNKNOWN
    _variant_t(const DECIMAL& decSrc) throw();                          // Creates a VT_DECIMAL
    _variant_t(BYTE bSrc) throw();                                      // Creates a VT_UI1

    _variant_t(char cSrc) throw();                                      // Creates a VT_I1
    _variant_t(unsigned short usSrc) throw();                           // Creates a VT_UI2
    _variant_t(unsigned long ulSrc) throw();                            // Creates a VT_UI4
    _variant_t(int iSrc) throw();                                       // Creates a VT_INT
    _variant_t(unsigned int uiSrc) throw();                             // Creates a VT_UINT
#if (_WIN32_WINNT >= 0x0501)
    _variant_t(__int64 i8Src) throw();                                  // Creates a VT_I8
    _variant_t(unsigned __int64 ui8Src) throw();                        // Creates a VT_UI8
#endif

    // Destructor
    //
    ~_variant_t() throw() ;

    // Extractors
    //
    operator short() const ;                           // Extracts a short from a VT_I2
    operator long() const ;                            // Extracts a long from a VT_I4
    operator float() const ;                           // Extracts a float from a VT_R4
    operator double() const ;                          // Extracts a double from a VT_R8
    operator CY() const ;                              // Extracts a CY from a VT_CY
    operator _bstr_t() const ;                         // Extracts a _bstr_t from a VT_BSTR
    operator IDispatch*() const ;                      // Extracts a IDispatch* from a VT_DISPATCH
    operator bool() const ;                            // Extracts a bool from a VT_BOOL
    operator IUnknown*() const ;                       // Extracts a IUnknown* from a VT_UNKNOWN
    operator DECIMAL() const ;                         // Extracts a DECIMAL from a VT_DECIMAL
    operator BYTE() const ;                            // Extracts a BTYE (unsigned char) from a VT_UI1
    operator VARIANT() const throw();

    operator char() const ;                            // Extracts a char from a VT_I1
    operator unsigned short() const ;                  // Extracts a unsigned short from a VT_UI2
    operator unsigned long() const ;                   // Extracts a unsigned long from a VT_UI4
    operator int() const ;                             // Extracts a int from a VT_INT
    operator unsigned int() const ;                    // Extracts a unsigned int from a VT_UINT
#if (_WIN32_WINNT >= 0x0501)
    operator __int64() const ;                         // Extracts a __int64 from a VT_I8
    operator unsigned __int64() const ;                // Extracts a unsigned __int64 from a VT_UI8
#endif

    // Assignment operations
    //
    _variant_t& operator=(const VARIANT& varSrc) ;
    _variant_t& operator=(const VARIANT* pSrc) ;
    _variant_t& operator=(const _variant_t& varSrc) ;

    _variant_t& operator=(short sSrc) ;                // Assign a VT_I2, or a VT_BOOL
    _variant_t& operator=(long lSrc) ;                 // Assign a VT_I4, a VT_ERROR or a VT_BOOL
    _variant_t& operator=(float fltSrc) ;              // Assign a VT_R4
    _variant_t& operator=(double dblSrc) ;             // Assign a VT_R8, or a VT_DATE
    _variant_t& operator=(const CY& cySrc) ;           // Assign a VT_CY
    _variant_t& operator=(const _bstr_t& bstrSrc) ;    // Assign a VT_BSTR
    _variant_t& operator=(const wchar_t* pSrc) ;       // Assign a VT_BSTR
    _variant_t& operator=(const char* pSrc) ;          // Assign a VT_BSTR
    _variant_t& operator=(IDispatch* pSrc) ;           // Assign a VT_DISPATCH
    _variant_t& operator=(bool boolSrc) ;              // Assign a VT_BOOL
    _variant_t& operator=(IUnknown* pSrc) ;            // Assign a VT_UNKNOWN
    _variant_t& operator=(const DECIMAL& decSrc) ;     // Assign a VT_DECIMAL
    _variant_t& operator=(BYTE bSrc) ;                 // Assign a VT_UI1

    _variant_t& operator=(char cSrc) ;                 // Assign a VT_I1
    _variant_t& operator=(unsigned short usSrc) ;      // Assign a VT_UI2
    _variant_t& operator=(unsigned long ulSrc) ;       // Assign a VT_UI4
    _variant_t& operator=(int iSrc) ;                  // Assign a VT_INT
    _variant_t& operator=(unsigned int uiSrc) ;        // Assign a VT_UINT
#if (_WIN32_WINNT >= 0x0501)
    _variant_t& operator=(__int64 i8Src) ;             // Assign a VT_I8
    _variant_t& operator=(unsigned __int64 ui8Src) ;   // Assign a VT_UI8
#endif

    // Comparison operations
    //
    bool operator==(const VARIANT& varSrc) const throw();
    bool operator==(const VARIANT* pSrc) const throw();

    bool operator!=(const VARIANT& varSrc) const throw();
    bool operator!=(const VARIANT* pSrc) const throw();

    // Low-level operations
    //
    void Clear() ;

    void Attach(VARIANT& varSrc) ;
    VARIANT Detach() throw();

    VARIANT& GetVARIANT() throw();
    VARIANT* GetAddress() ;

    void ChangeType(VARTYPE vartype, const _variant_t* pSrc = NULL) ;

    void SetString(const char* pSrc) ; // used to set ANSI string
};