CODEWITHSUNDEEP
visual-c++comvariantole-automation
Mehul
Mehul

Reputation: 155

What is exactly VARIANT data structure?

I am learning Microsoft OLE Automation and COM and it use VARIANT to pass data. I have read that it is union data structure but did not find enough information regarding this.

It would be helpful to me understand more about VARIANT as I am new to Automation and COM ?

Upvotes: 1

Views: 4539

Answers (2)

Simon Mourier
Simon Mourier

Reputation: 139157

COM Automation defines a set of types that it knows how to marshal through thread or process boundaries.

It means there is no need for custom proxy/stubs if you restrict your interfaces to use only those types, and you describe your interface with a type library (most development tools, such as Visual Studio, do that automatically).

Those types are described here: VARENUM Enumeration.

The VARIANT type is itself an automation type, it's a struct that can contain any one of the other automation types.

COM Automation appeared with the Visual Basic development environment (up to version 6, before VB.NET). VB/VBA defines the same types (including Variant).

Upvotes: 4

Florent B.
Florent B.

Reputation: 42528

A VARIANT is 16 bytes long. The first two bytes define the data type that the variant holds:

https://msdn.microsoft.com/en-us/library/windows/desktop/ms221170(v=vs.85).aspx

The second half of the VARIANT holds the variable’s content. For more informations:

https://msdn.microsoft.com/en-gb/library/windows/desktop/ms221627(v=vs.85).aspx

Upvotes: 2

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