3.2. Pointers

In Caterpillar, pointers are emulated using special structs that behave according to the underlying architecture. This feature allows you to model pointer-like behavior in your data structures, making it easier to work with architecture-dependent data formats. Pointers in this context refer to memory addresses, often used to reference other data structures or objects.

To define a pointer in Caterpillar, you can use the * operator in conjunction with a field, which indicates that the field should behave like a pointer to another data type. Here’s an example:

@struct
class Format:
    name: uintptr *CString(...)      # Using multiplication to model a pointer

The behavior of a pointer depends on the architecture it is being unpacked on. For example, on an x86 architecture, the pointer will be interpreted accordingly based on how pointers are represented in memory for that platform.

>>> data = b"\x00\x00\x00\x04Hello, World!\x00"
>>> o = unpack(Format, data, _arch=x86)
Format(name=<str* 0x4>)
>>> _.name.obj
'Hello, World!'

The pointer behavior is facilitated by the pointer class in Caterpillar. This class acts as a standard integer that stores the parsed model object (the referenced data). The pointer itself is an integer value, but it also holds a reference to the object it points to.