_variant_tThis class is a wrapper for the Automation Variant data type. It provides memory allocation and deallocation, and calls SysAllocString and SysFreeString when appropriate. _bstr_tThis class is a wrapper for the Automation Bstr data type. It provides memory allocation and deallocation, and calls VariantInit and VariantClear when appropriate.
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VariantInit(&varSrc);
varSrc.bstrVal = (BSTR)sz;
你可以查看MSDN
10 for the joining.
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呵呵,好像msdn不是书本:)