在VC ++中将可选参数传递给COM函数

I have an MFC wrapper over a COM object. There is a function that takes a large number of options, which are mostly optional. How do I pass some arguments but not others?

我在COM对象上有一个MFC包装器。有一个函数需要大量选项,这些选项大多是可选的。我如何传递一些参数但不传递其他参数?

For what it's worth, the optional arguments are listed as VARIANT*.

对于它的价值,可选参数列为VARIANT *。

Below is the code

以下是代码

CComVariant vFalse = false;
CApplication application;

{
    application.CreateDispatch(_T("Word.Application"));

    CDocuments documents = application.get_Documents();       

    CComVariant vFilename = _T("c:\\temp\\test.rtf");
    CComVariant vNothing;
    CComVariant vEmpty = _T("");
    CComVariant vOpenFormat = 0;
    application.put_Visible(TRUE);

    //
    // THIS FUNCTION has a number of optional arguments
    //
    LPDISPATCH pDocument = documents.Open(&vFilename, &vFalse, &vFalse, &vFalse, &vEmpty, &vEmpty, &vFalse, &vEmpty, &vEmpty, &vOpenFormat, &vOpenFormat, &vFalse, &vFalse, &vOpenFormat, &vFalse, &vFalse);
}
application.Quit(&vFalse, NULL, NULL);

2 个解决方案

#1

To skip an optional parameter in a COM method pass a VARIANT of type VT_ERROR and the error code must by DISP_E_PARAMNOTFOUND.

要跳过COM方法中的可选参数,请传递VT_ERROR类型的VARIANT,错误代码必须通过DISP_E_PARAMNOTFOUND。

CComVariant vtOptional;
vtOptional.vt = VT_ERROR;
vtOptional.scode = DISP_E_PARAMNOTFOUND;

Now you can use vtOptional as a parameter you don't want to specify if the parameter is optional.

现在,您可以使用vtOptional作为参数,如果参数是可选的,则不希望指定该参数。

Here is the official word on this: "How to pass optional parameters when you call a function in Visual C++"

以下是关于此的官方说法:“在Visual C ++中调用函数时如何传递可选参数”

#2

An unspecified variant is normally VT_EMPTY:

未指定的变体通常是VT_EMPTY:

_variant_t vtEmpty(VT_EMPTY);

You obviously have written the CDocuments and CApplication wrappers around the COM interfaces, so you could specify the optional parameters as having default value of vtEmpty.

您显然已经在COM接口周围编写了CDocuments和CApplication包装器,因此您可以将可选参数指定为具有默认值vtEmpty。

#1