visual-c++ - 如何将“双”转换为“变体”

Question

在我通过 VC 2012 的应用程序中，就绪函数需要“VARIANT”值作为输入。我有一个“双”变量。以下是我厌倦了无效的转换。在网上搜索并没有找到答案。请指教。谢谢。

   double db=19;
   VARIANT v;
   v.dblVal=19;

标签： visual-c++type-conversion

Answer 1

下面来自窗口文件之一的评论将简要介绍支持的VARIANT数据类型

/*
 * VARENUM usage key,
 *
 * * [V] - may appear in a VARIANT
 * * [T] - may appear in a TYPEDESC
 * * [P] - may appear in an OLE property set
 * * [S] - may appear in a Safe Array
 * * [C] - supported by class _variant_t
 *
 *
 *  VT_EMPTY            [V]   [P]        nothing
 *  VT_NULL             [V]   [P]        SQL style Null
 *  VT_I2               [V][T][P][S][C]  2 byte signed int
 *  VT_I4               [V][T][P][S][C]  4 byte signed int
 *  VT_R4               [V][T][P][S][C]  4 byte real
 *  VT_R8               [V][T][P][S][C]  8 byte real
 *  VT_CY               [V][T][P][S][C]  currency
 *  VT_DATE             [V][T][P][S][C]  date
 *  VT_BSTR             [V][T][P][S][C]  OLE Automation string
 *  VT_DISPATCH         [V][T][P][S][C]  IDispatch *
 *  VT_ERROR            [V][T]   [S][C]  SCODE
 *  VT_BOOL             [V][T][P][S][C]  True=-1, False=0
 *  VT_VARIANT          [V][T][P][S]     VARIANT *
 *  VT_UNKNOWN          [V][T]   [S][C]  IUnknown *
 *  VT_DECIMAL          [V][T]   [S][C]  16 byte fixed point
 *  VT_I1                  [T]           signed char
 *  VT_UI1              [V][T][P][S][C]  unsigned char
 *  VT_UI2                 [T][P]        unsigned short
 *  VT_UI4                 [T][P]        unsigned short
 *  VT_I8                  [T][P]        signed 64-bit int
 *  VT_UI8                 [T][P]        unsigned 64-bit int
 *  VT_INT                 [T]           signed machine int
 *  VT_UINT                [T]           unsigned machine int
 *  VT_VOID                [T]           C style void
 *  VT_HRESULT             [T]           Standard return type
 *  VT_PTR                 [T]           pointer type
 *  VT_SAFEARRAY           [T]          (use VT_ARRAY in VARIANT)
 *  VT_CARRAY              [T]           C style array
 *  VT_USERDEFINED         [T]           user defined type
 *  VT_LPSTR               [T][P]        null terminated string
 *  VT_LPWSTR              [T][P]        wide null terminated string
 *  VT_FILETIME               [P]        FILETIME
 *  VT_BLOB                   [P]        Length prefixed bytes
 *  VT_STREAM                 [P]        Name of the stream follows
 *  VT_STORAGE                [P]        Name of the storage follows
 *  VT_STREAMED_OBJECT        [P]        Stream contains an object
 *  VT_STORED_OBJECT          [P]        Storage contains an object
 *  VT_BLOB_OBJECT            [P]        Blob contains an object
 *  VT_CF                     [P]        Clipboard format
 *  VT_CLSID                  [P]        A Class ID
 *  VT_VECTOR                 [P]        simple counted array
 *  VT_ARRAY            [V]              SAFEARRAY*
 *  VT_BYREF            [V]              void* for local use
 */

您应该使用_variant_t而不是VARIANT。下面的代码会将您的双精度值转换为变体，

_variant_t var(10.52);