Question

_variant_t怎么当函数用呢

_variant_t是一个封装类，但是为什么可以当函数使用呢？例如m_pRecordset->PutCollect("Name", _variant_t(m_Name));难道c++允许这样使用类吗？如果是类型转换的话，为什么不是(_variant_t)m_Name

Answer 1

使用参数列表来构造对象啊 参考msdn
Construction

_variant_t Constructs a _variant_t object.
Microsoft Specific

_variant_t( ) throw( );

_variant_t( const VARIANT& varSrc ) throw( _com_error );

_variant_t( const VARIANT* pVarSrc ) throw( _com_error );

_variant_t( const _variant_t& var_t_Src ) throw( _com_error );

_variant_t( VARIANT& varSrc, bool fCopy ) throw( _com_error );

_variant_t( short sSrc, VARTYPE vtSrc = VT_I2 ) throw( _com_error );

_variant_t( long lSrc, VARTYPE vtSrc = VT_I4 ) throw( _com_error );

_variant_t( float fltSrc ) throw( );

_variant_t( double dblSrc, VARTYPE vtSrc = VT_R8 ) throw( _com_error );

_variant_t( const CY& cySrc ) throw( );

_variant_t( const _bstr_t& bstrSrc ) throw( _com_error );

_variant_t( const wchar_t *wstrSrc ) throw( _com_error );

_variant_t( const char* strSrc ) throw( _com_error );

_variant_t( bool bSrc ) throw( );

_variant_t( IUnknown* pIUknownSrc, bool fAddRef = true ) throw( );

_variant_t( IDispatch* pDispSrc, bool fAddRef = true ) throw( );

_variant_t( const DECIMAL& decSrc ) throw( );

_variant_t( BYTE bSrc ) throw( );

Answer 2

不是强制转化，应该是构造一个对象