On Sun, May 6, 2018 at 2:17 AM, Brad M <thebigwu...@gmail.com> wrote:
>
> Say I have an array of values, say addresses or int produced by a c module/
> c function that's in a DLL , how do I pass that array back to
> the python code?
C arrays are passed and returned automatically as pointers to the
first element. The array length has to be passed separately, unless
there's a known sentinel value.
A simple pattern is to let the caller allocate the array and pass a
pointer and the length. This gives the caller explicit control over
the lifetime of the array, which is especially simple for ctypes since
it uses reference-counted objects.
Say you have a function in C such as the following:
int
DLLAPI
get_data(int *data, size_t length)
{
size_t i;
for (i=0, i < length; i++) {
if (do_something(i, &data[i]) == -1) {
return -1; /* failure */
}
}
return 0; /* success */
}
In Python, set up and call this function as follows:
import ctypes
mydll = ctypes.CDLL('mydll')
# setup
mydll.get_data.argtypes = (
ctypes.POINTER(ctypes.c_int), # data
ctypes.c_size_t) # length
# call
data = (ctypes.c_int * 10)()
status = mydll.get_data(data, len(data))
if status == -1:
raise MyDllException('get_data: ...')
for i, value in enumerate(data):
result = do_something_else(i, value)
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