ctypes.ArgumentError: Don't know how to convert parameter

Question

I define a function in C library as follows:

int* Test(char *str1,int id1,char *str2,float val,float *ls)

I want to use it in python so I write the following python code:

str1 = 'a'
str2 = 'b'
id1 = 0
val = 1.0
system('g++ -c -fPIC libtraj.cpp -o test.o')
system('g++ -shared -Wl,-soname,test.so -o test.so test.o')
lib = cdll.LoadLibrary('./test.so')
num_item = 100000
ls = (ctypes.c_float * num_item)()
lib.Test.restype = ndpointer(dtype=ctypes.c_int, shape=(num_item,))
lib.Test.argtypes = [c_char_p]
a = create_string_buffer(str1)
b = create_string_buffer(str2)
ls_id = lib.Test(a,id1,b,val,ctypes.byref(ls))

Then I run this python program. I met with error saying:

ls_id = lib.Test(a,id1,b,val,ctypes.byref(ls))
ctypes.ArgumentError: argument 4: <type 'exceptions.TypeError'>: Don't know how to convert parameter 4

What's wrong with my code? Thank you all for helping me!!!

Jevons

Try: lib.Test.argtypes = [c_char_p, c_int, c_char_p, c_float, POINTER(c_float)] (all defined by ctypes). – Meaningless

Also ndpointer seems to be related to numpy....if so, there's a great chance that mixing it with ctypes won't work. – Meaningless

Answer 1

The solution provided by @CristiFati solves my problem. I just copy his answer in the comments and present here. Thank you @CristiFati.

Try:

lib.Test.argtypes = [c_char_p, c_int, c_char_p, c_float, POINTER(c_float)] # (all defined by ctypes)

Jevons