COM IDL 定义中 [in, out] 和 [out, retval] 之间的差异
在我使用的一些 IDL 中，我注意到有 2 个用于标记方法返回值的约定 - [in, out] 和 [out, retval]。
当有多个返回值时，似乎使用[in, out]，例如：
HRESULT MyMethod(
[in] long InputParam,
[in, out] long* OutputParam1,
[in, out] long* OutputParam2
);
当只有一个返回值时，似乎使用[out, retval]返回值，例如：
HRESULT MyMethod2(
[in] long InputParam,
[out, retval] long* OutputParam1
);
这是 COM IDL 约定还是只是我正在使用的代码中的约定？
从这两种符号生成的代码是否存在功能差异，或者它们是否完全可以互换？
In some of the IDL I work with I have noticed that there are 2 conventions for marking return values in methods - [in, out] and [out, retval].
It appears that [in, out] is used when there are multiple return values, for example:
HRESULT MyMethod(
[in] long InputParam,
[in, out] long* OutputParam1,
[in, out] long* OutputParam2
);
It appears that [out, retval] is used when there is only a single return value, for example:
HRESULT MyMethod2(
[in] long InputParam,
[out, retval] long* OutputParam1
);
Is this a COM IDL convention or just a convention in the code I am working with?
Is there a functional difference in the code that will be generated from the 2 notations, or are they completely interchangeable?
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[in, out]表示调用方法时传递了有效值，并且方法返回成功时（指针指向的位置）存在有效值。[out]表示调用方法时指向的值可以是任何值，但在方法返回成功时才有效。[out]和[in, out]参数都必须是指针 - 它们的值未更改且有效，并且有效性要求仅适用于它们指向的变量。[out, retval]是一个语法糖，指示在创建本机 COM 支持包装器时，应将这个参数转换为返回值。例如变为
如果不标记
[retval]，则包装器将包含具有原始签名的方法：只有最后一个
[out]参数可以标记为[输出，retval]。[in, out]参数不能标记为[retval]。[in, out]means that a valid value is passed when the method is called and a valid value is there (where the pointer points) when the method returns success.[out]means that the value pointed to can be whatever when the method is called but it will be valid when the method returns success. Both[out]and[in, out]parameters must be pointers - their values are unchanged and valid and the validity requirements only apply to the variables they point to.[out, retval]is a syntactic sugar to indicate that when creating a Native COM Support wrapper this very parameter should be converted to a return value. For examplebecomes
If you don't mark it
[retval]the wrapper will contain a method with the original signature:Only the last one
[out]parameter can be marked as[out, retval].[in, out]parameters can't be marked as[retval].另一个区别是它在 .NET 代码的 PIA 中的显示方式。
[out, ret] 将在 .NET 中显示为返回值。
[out] 将显示 .NET 中方法的参数。
Another difference is how this will show up in a PIA in .NET code.
[out, ret] will show up as a return value in .NET.
[out] will show up an argument on the method in .NET.