CODEWITHSUNDEEP
pythonctypes
Sbmueller
Sbmueller

Reputation: 103

Ctypes pointer on element in ctypes array

Is there a way to get a pointer to an element in the middle of an ctypes array? Example:

lib = ctypes.cdll.LoadLibrary('./lib.so')
arr = (ctypes.c_int32 * 100)()
lib.foo(arr)

Now I don't want to call foo with a pointer to the first element of arr, but on the 10th. That would be equivalent to C notation &arr[9]:

lib.foo(&arr[9])

Is there a smart way to do this?

Upvotes: 4

Views: 1273

Answers (1)

Mark Tolonen
Mark Tolonen

Reputation: 177600

byref has an optional parameter to add a byte offset to the address.

test.dll (Windows)

__declspec(dllexport) int foo(int* arr)
{
    return *arr;
}

Example:

>>> from ctypes import *
>>> lib = CDLL('test')
>>> arr = (c_int * 100)(*range(100))
>>> arr[9]
9
>>> lib.foo(arr)
0
>>> lib.foo(byref(arr,sizeof(c_int) * 9))
9

Upvotes: 6

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