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pythonctypes
jett chen
jett chen

Reputation: 1173

How to translate C double two-dim data using python ctypes?

I try use python ctypes call a dll and translate api in python code. But I meet a function that have two-dimensional array and I dont know how to translate it now.I had forgot my C++&C language. TCHAR is a type like this char *p.

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Upvotes: 1

Views: 76

Answers (1)

Mark Tolonen
Mark Tolonen

Reputation: 177891

.argtypes for the function would be:

lmc1_AddCurveToLib.argtypes = POINTER(c_double * 2), c_int, c_char_p, c_int, c_int

Here's a complete example:

test.c

#include <windows.h>
#include <stdio.h>

#ifdef _WIN32
#   define API __declspec(dllexport)
#else
#   define API
#endif

API int lmc1_AddCurveToLib(double ptBuf[][2], int ptNum, TCHAR* pEntName, int nPenNo, BOOL bHatch) {
    printf("%s %d %d\n", pEntName, nPenNo, bHatch);
    for(int i = 0; i < ptNum; i++)
        printf("ptBuf[%d][0] = %lf, ptBuf[%d][1] = %lf\n", i, ptBuf[i][0], i, ptBuf[i][1]);
    return 123;
}

test.py

import ctypes as ct

dll = ct.CDLL('./test')
# POINTER(c_double * 2) is equivalent to C (*double)[2] or double[][2], "A pointer to two doubles".
dll.lmc1_AddCurveToLib.argtypes = ct.POINTER(ct.c_double * 2), ct.c_int, ct.c_char_p, ct.c_int, ct.c_int
dll.lmc1_AddCurveToLib.restype = ct.c_int

# C equivalent: double arr[3][2] = {{1.1,2.2}, {3.3,4.4}, {5.5,6.6}};
# Note that *2*3 below is required order and opposite of C to
# achieve the same memory layout.
arr = (ct.c_double * 2 * 3)((1.1,2.2),(3.3,4.4),(5.5,6.6))

print(dll.lmc1_AddCurveToLib(arr, len(arr), b'SomeName', 5, True))

Output:

SomeName 5 1
ptBuf[0][0] = 1.100000, ptBuf[0][1] = 2.200000
ptBuf[1][0] = 3.300000, ptBuf[1][1] = 4.400000
ptBuf[2][0] = 5.500000, ptBuf[2][1] = 6.600000
123

Upvotes: 1

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