COM IDL定义中的[in，out]和[out，retval]之间的差异 [英] Differences between [in, out] and [out, retval] in COM IDL definitions

问题描述

在一些IDL中，我注意到有两种方法标记返回值的惯例 - [in，out] 和

当有多个返回值时使用，例如：

  HRESULT MyMethod（
 [in] long InputParam，
 [in，out] long * OutputParam1，
 [in，out] long * OutputParam2 
）; 
  

看起来 [out，retval] 当只有一个返回值时使用，例如：

  HRESULT MyMethod2（
 [in] long InputParam ，
 [out，retval] long * OutputParam1 
）; 
  

这是COM IDL约定还是我正在使用的代码中的约定？

在代码中是否有两个符号产生的功能差异，还是完全可以互换？

解决方案

[in，out] 表示当方法被调用并且有效值存在时传递一个有效值点）当方法返回成功。 [out] 表示指向的值可以是调用方法时的值，但在方法返回成功时将有效。参数必须是指针 - 它们的值不变并且有效，并且有效性是有效的。 [out] 和

[out，retval] 是一个语法糖，用于表示当创建一个本地COM支持包装器这个非常参数应该转换为一个返回值。例如

  HRESULT MyMethod（[out] long * OutParam1，[out，retval] long * OutParam2）; 
  

成为

  long IWrappedInterface :: MyMethod（long * OutParam1）; 
  

如果您不将其标记 [retval] 包装器将包含具有原始签名的方法：

  HRESULT IWrappedInterface :: MyMethod（long * OutParam1，long * OutParam2 ）; 
  

只有最后一个 [out] 可以标记为 [out，retval] 。 [in，out] 参数不能标记为 [retval] 。

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?

解决方案

[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 example

HRESULT MyMethod( [out] long* OutParam1, [out, retval] long* OutParam2 );

becomes

long IWrappedInterface::MyMethod( long* OutParam1 );

If you don't mark it [retval] the wrapper will contain a method with the original signature:

HRESULT IWrappedInterface::MyMethod( long* OutParam1, long* OutParam2 );

Only the last one [out] parameter can be marked as [out, retval]. [in, out] parameters can't be marked as [retval].

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