Python, ctypes, multi-Dimensional Array

Question

I have structure in Python code and in C code. I fill these fields

(\"bones_pos_vect\",((c_float*4)*30)),
(\"bones_rot_quat\",((c_float*4)*30))

Answer 1

Here's an example of how you can use a multidimensional array with Python and ctypes.

I wrote the following C code, and used gcc in MinGW to compile this to slib.dll:

#include 

typedef struct TestStruct {
    int     a;
    float   array[30][4];
} TestStruct;

extern void print_struct(TestStruct *ts) {
    int i,j;
    for (j = 0; j < 30; ++j) {
        for (i = 0; i < 4; ++i) {
            printf("%g ", ts->array[j][i]);
        }
        printf("\n");
    }
}

Note that the struct contains a 'two-dimensional' array.

I then wrote the following Python script:

from ctypes import *

class TestStruct(Structure):
    _fields_ = [("a", c_int),
                ("array", (c_float * 4) * 30)]

slib = CDLL("slib.dll")
slib.print_struct.argtypes = [POINTER(TestStruct)]
slib.print_struct.restype = None

t = TestStruct()

for i in range(30):
    for j in range(4):
        t.array[i][j] = i + 0.1*j

slib.print_struct(byref(t))

When I ran the Python script, it called the C function, which printed out the contents of the multidimensional array:

C:\>slib.py
0.1 0.2 0.3 0.4
1.1 1.2 1.3 1.4
2.1 2.2 2.3 2.4
3.1 3.2 3.3 3.4
4.1 4.2 4.3 4.4
5.1 5.2 5.3 5.4
... rest of output omitted

I've used Python 2, whereas the tags on your question indicate that you're using Python 3. However, I don't believe this should make a difference.