How to Use structs in COM interfaces when Automation
compatibility is not an issue?






How to Use structs in COM interfaces when Automation compatibility is not an issue?..

Answer / krishna akkulu

Structs, also known as User Defined Types (UDTs), can be
used in Automation- compatible interfaces
An Automation- compatible struct may contain only primitive
Automation types as its members.

Nesting structs is not allowed, but VARIANT is allowed thus
enabling nested structs (you can store a struct in a
VARIANT).

In order for a struct to be usable for Automation-
compatible interfaces, the struct must be described in a
type library and it must be declared with its own GUID:

[uuid(21602F40-CC62-11d4-AA2B-00A0CC39CFE0)]
struct MyStruct
{
[helpstring("A long value")]
long nLongValue;

[helpstring("A string")]
BSTR bstrStringValue;
};

// Later in the IDL file
[uuid(...), version(...), helpstring(...)]
library MyLib
{
...
struct MyStruct;
};
For more info see : http://vcfaq.mvps.org/com/4.htm

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