# Introduction

All public functions in the C API are prefixed with py_ in pocketpy.h.

pocketpy works with opaque references. py_Ref is used to reference objects in the virtual machine. It is your responsibility to ensure a reference is valid before using it. See following reference types:

/// A generic reference to a python object.
typedef py_TValue* py_Ref;
/// A reference which has the same lifespan as the python object.
typedef py_TValue* py_ObjectRef;
/// A global reference which has the same lifespan as the VM.
typedef py_TValue* py_GlobalRef;
/// A specific location in the value stack of the VM.
typedef py_TValue* py_StackRef;
/// An item reference to a container object. It invalidates when the container is modified.
typedef py_TValue* py_ItemRef;
/// An output reference for returning a value.
typedef py_TValue* py_OutRef;

You can store python objects into "stack" or "register". We provide 8 registers and you can get references to them by py_reg(). Also, py_retval() is a special register that is used to store the return value of a py_CFunction. Registers are shared so they could be overwritten easily. If you want to store python objects across function calls, you should store them into the stack via py_push() and py_pop().

You can do conversions between C types and python objects using the following functions:

Mark a function that can raise an exception on failure.

• If the function returns bool, then false means an exception is raised.
• If the function returns int, then -1 means an exception is raised.

Mark a function that can store a value in py_retval() on success.