==这是Delphi帮助注明:
The OleVariant type exists on both the Windows and Linux platforms. The main difference between Variant and OleVariant is that Variant can contain data types that only the current application knows what to do with. OleVariant can only contain the data types defined as compatible with OLE Automation which means that the data types that can be passed between programs or across the network without worrying about whether the other end will know how to handle the data.
When you assign a Variant that contains custom data (such as a Delphi string, or a one of the new custom variant types) to an OleVariant, the runtime library tries to convert the Variant into one of the OleVariant standard data types (such as a Delphi string converts to an OLE BSTR string). For example, if a variant containing an AnsiString is assigned to an OleVariant, the AnsiString becomes a WideString. The same is true when passing a Variant to an OleVariant function parameter.
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varisnull 是用来判断 OleVariant 返回值是否为null 可以用 null;
varIsEmpty 是用来判断 OleVariant 返回值是否为Empty 可以用EmptyParam或 unassigned来斌OleVariant为empty
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