Day: July 5, 2013

VBA Internals: Variant Variables and Pointers in Depth

Pointers and memory for Variant variables

In the Component Object Model (COM) Automation framework, the VARIANT structure provides a wrapper for passing around any type of data, and a suite of manipulation functions facilitate using the VARIANT as a platform-level dynamically-typed variable. I say platform-level because the structures, enumerations, and functions that implement VARIANTs exist at the Windows API level. Any language -- including those that are not dynamically typed -- can use the API to accomplish something like dynamic types.

VBA does provide dynamically typed variables, and calls them Variants, just like the supporting structures in the COM API. When writing VBA code you never have to call the API functions like VarAdd or VarXor. The compiler and runtime do it for you behind the scenes. But when you pop the hood and start directly working with the bits and bytes of Variant variables and pointers it's important to know what you're really dealing with -- namely, a COM VARIANT structure.

The details of the layout of the 16 bytes in the VARIANT structure are covered in detail in What's in a variable. The full code of the memory utility functions used in the examples in this post are included in Scalar Variables and Pointers in Depth.

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