Best way to return a struct of strings?

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Scott Markwell - 03 Apr 2006 21:15 GMT

I want to pass back a group of data to a caller. What I am currently
doing involves returning a pointer to a struct defined in IDL and
available in the TLB. The thing is this gets messy w/ managed .NET code
involving messing w/ a System.IntPtr. Will managed code properly
release a structure with BSTR's located within the struct during garbage
collection? Is there a better way then providing a function for
unmanaged users to call to release a object?

typedef struct DataResult
{
BSTR infoA;
BSTR infoB;
BSTR infoC;
long infoD;
boolean infoE;
}DataResult;

[
object,
]
interface IFoo:IUnknown
{
HRESULT GetData([out,retval]DataResult **dataOut);
HRESULT FreeData([in,out]DataResult **release);
};

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Scott M. - 03 Apr 2006 22:29 GMT

Why not just make a class with a method that returns what you need? Strings
are classes (reference types) and are stored on the heap anyway, so what do
you gain by using a structure?

>I want to pass back a group of data to a caller. What I am currently doing
>involves returning a pointer to a struct defined in IDL and available in
[quoted text clipped - 21 lines]
> HRESULT FreeData([in,out]DataResult **release);
> };

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Scott Markwell - 03 Apr 2006 23:43 GMT

Ease of use for a caller. Instead of building their own local format.
Basically the goal is to pass back some structure that is convent for a
caller from C++ or managed code and provides all the data from a single
record in a single type.

> Why not just make a class with a method that returns what you need? Strings
> are classes (reference types) and are stored on the heap anyway, so what do
[quoted text clipped - 25 lines]
>> HRESULT FreeData([in,out]DataResult **release);
>> };

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Scott Markwell - 04 Apr 2006 01:04 GMT

Think I've found what I need.
System.Runtime.InteropServices.Marshal.DestroyStructure should handle
the BSTR's and call SysFreeString on them.

> Ease of use for a caller. Instead of building their own local format.
> Basically the goal is to pass back some structure that is convent for a
[quoted text clipped - 30 lines]
>>> HRESULT FreeData([in,out]DataResult **release);
>>> };

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Best way to return a struct of strings?

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