Question

Assume p = ctypes.cast("foo", ctypes.POINTER(ctypes.c_char)).

Thus, we have p.contents.value == "f".

How can I directly access and manipulate (e.g. increment) the pointer? E.g. like (p + 1).contents.value == "o".

Answer 1

You have to use indexing:

>>> p = ctypes.cast("foo", ctypes.POINTER(ctypes.c_char))
>>> p[0]
'f'
>>> p[1]
'o'
>>> p[3]
'\x00'

Have a look at ctypes documentation to find out more about using pointers.

UPDATE: It seems that it’s not what you need. Let’s, then, try another approach: first cast the pointer to void, increment it and then cast it back to LP_c_char:

In [93]: p = ctypes.cast("foo", ctypes.POINTER(ctypes.c_char))

In [94]: void_p = ctypes.cast(p, ctypes.c_voidp).value+1

In [95]: p = ctypes.cast(void_p, ctypes.POINTER(ctypes.c_char))

In [96]: p.contents
Out[96]: c_char('o')

Maybe it’s not elegant but it works.