I am using ctypes to pass an array pointer to a dll and return a pointer to an array of doubles that was created using malloc in the dll. On return to Python, I need a fast way to convert the pointer to an array or Python list.
I can use this list comp, but it's slow because there are 320,000 data points:
list_of_results = [ret_ptr[i] for i in range(320000)]
Ideally I would create the array in Python and pass it to the dll, but I have to create it using malloc in the dll because this is a dynamic array where I don't know beforehand how many data elements there will be (although the return pointer also returns the number of data elements, so I know how many there are on return to Python) -- I use realloc to extend the array size dynamically in the dll; I can use realloc with a Python array, but a call to free() at the end is not guaranteed to work.
Here is the relevant Python code:
CallTest = hDLL.Main_Entry_fn
CallTest.argtypes = [ctypes.POINTER(ctypes.c_double), ctypes.c_int64]
CallTest.restype = ctypes.POINTER(ctypes.c_double)
ret_ptr = CallTest(DataArray, number_of_data_points)
list_of_results = [ret_ptr[i] for i in range(320000)]
So my question is: what is the fastest way to convert a pointer returned from a dll to a Python list or array? The method shown above is too slow.
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Link to original article：https://stackoverflow.com/questions/48913932/ctypes-fast-way-to-convert-a-return-pointer-to-an-array-or-python-list