Day: May 31, 2013
VBA Internals: String Variables and Pointers in Depth
This is the next installment of a series of deep-dives into the structure and implementation of variables in Visual Basic for Applications. For the previous posts, see the following:
- What’s in a variable - Categories of variables in VBA, by implementation
- Getting Pointers - Overview of how to obtain pointers in VBA
- Scalar Variables and Pointers in Depth - Details of numeric scalar variables and pointers
In this post, I will cover the details of string variables and pointers. See Scalar Variables and Pointers in Depth for additional background and for the code for the utility functions HexPtr and Mem_ReadHex.
Pointers and memory for string variables
Even though string variables are treated semantically as value types, they are reference types by implementation. The contents of a string variable is actually a pointer to another memory location where the actual string characters are stored. With VBA we can either get the address to the variable itself using VarPtr, or we can go straight to the start of the character buffer by using StrPtr. For a variable declared as a String, then, directly reading the memory at the address returned by VarPtr should give you the same pointer value as calling StrPtr.