如何将2d数组从Python传递到C? [英] How to pass a 2d array from Python to C?
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问题描述
我正在尝试使用ctypes将2d数组从Python传递到C. 数组dtype是uint16. 我写了一个简单的代码只是为了了解它是如何工作的:
C:
#include <stdint.h>
__declspec(dllexport) uint16_t Test(uint16_t **arr)
{
return (arr[5][5]);
}
Python:
import numpy as np
from ctypes import cdll
import ctypes
from numpy.ctypeslib import ndpointer
_p = ndpointer(dtype=np.uint16, ndim=2, shape=(10, 10), flags='C')
mydll = cdll.LoadLibrary("mydll.dll")
_func = mydll.Test
_func.argtypes = [_p]
_func.restypes = ctypes.c_uint16
data = np.empty([10, 10], dtype=np.uint16)
data[5, 5] = 5
print(_func(data))
我收到OSError:访问冲突读取为0xFFFFFFFFFFFFFFFFFFFFFFFFFF 我在做什么错以及如何解决?
解决方案
列出 [SO]:通过ctypes在Python中调用C函数，但函数返回的值不正确(@CristiFati的回答)(重复)，这恰好也侵犯了 NumPy .
换句话说，您具有 未定义行为 ，因为 argtypes 必须是 CTypes 类型(不是 NumPy ).
下面是您代码的修改版本，可以正常工作.
dll00.c :
#include <stdint.h>
#if defined(_WIN32)
# define DLL00_EXPORT_API __declspec(dllexport)
#else
# define DLL00_EXPORT_API
#endif
#if defined(__cplusplus)
extern "C" {
#endif
DLL00_EXPORT_API uint16_t dll00Func00(uint16_t **ppArr);
#if defined(__cplusplus)
}
#endif
uint16_t dll00Func00(uint16_t **ppArr) {
return ppArr[5][5];
}
code00.py :
#!/usr/bin/env python3
import sys
import ctypes as ct
import numpy as np
DLL_NAME = "./dll00.dll"
def main():
UI16Ptr = ct.POINTER(ct.c_uint16)
UI16PtrPtr = ct.POINTER(UI16Ptr)
dll00 = ct.CDLL(DLL_NAME)
dll00Func00 = dll00.dll00Func00
dll00Func00.argtypes = [UI16PtrPtr]
dll00Func00.restype = ct.c_uint16
dim0 = 10
dim1 = 10
np_arr_2d = np.empty([dim0, dim1], dtype=np.uint16)
np_arr_2d[5][5] = 5
print(np_arr_2d)
# The "magic" happens in the following (3) lines of code
ct_arr = np.ctypeslib.as_ctypes(np_arr_2d)
UI16PtrArr = UI16Ptr * ct_arr._length_
ct_ptr = ct.cast(UI16PtrArr(*(ct.cast(row, UI16Ptr) for row in ct_arr)), UI16PtrPtr)
res = dll00Func00(ct_ptr)
print("\n{0:s} returned: {1:d}".format(dll00Func00.__name__, res))
if __name__ == "__main__":
print("Python {0:s} {1:d}bit on {2:s}\n".format(" ".join(item.strip() for item in sys.version.split("\n")), 64 if sys.maxsize > 0x100000000 else 32, sys.platform))
print("NumPy: {0:s}\n".format(np.version.version))
main()
print("\nDone.")
输出:
[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q058727931]> sopr.bat *** Set shorter prompt to better fit when pasted in StackOverflow (or other) pages *** [prompt]> "c:\Install\x86\Microsoft\Visual Studio Community\2017\VC\Auxiliary\Build\vcvarsall.bat" x64 ********************************************************************** ** Visual Studio 2017 Developer Command Prompt v15.9.17 ** Copyright (c) 2017 Microsoft Corporation ********************************************************************** [vcvarsall.bat] Environment initialized for: 'x64' [prompt]> dir /b code00.py dll00.c [prompt]> cl /nologo /DDLL dll00.c /link /NOLOGO /DLL /OUT:dll00.dll dll00.c Creating library dll00.lib and object dll00.exp [prompt]> dir /b code00.py dll00.c dll00.dll dll00.exp dll00.lib dll00.obj [prompt]> "e:\Work\Dev\VEnvs\py_064_03.07.03_test0\Scripts\python.exe" code00.py Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] 64bit on win32 NumPy: 1.16.2 [[19760 5277 632 0 32464 5280 632 0 111 114] [ 107 92 68 101 118 92 86 69 110 118] [ 115 92 112 121 95 48 54 52 95 48] [ 51 46 48 55 46 48 51 95 116 101] [ 115 116 48 92 108 105 98 92 115 105] [ 116 101 45 112 97 5 107 97 103 101] [ 115 92 110 117 109 112 121 92 116 101] [ 115 116 105 110 103 92 95 112 114 105] [ 118 97 116 101 92 110 111 115 101 116] [ 101 115 116 101 114 46 112 121 0 0]] dll00Func00 returned: 5 Done.
所有这些时髦转换的说明可以在 [SO]:使用ctypes传递和获取C函数数组的问题(@CristiFati的回答).
I'm trying to pass a 2d array from Python to C, using ctypes. The array dtype is uint16. I wrote a simple code just to understand how it works:
C:
#include <stdint.h>
__declspec(dllexport) uint16_t Test(uint16_t **arr)
{
return (arr[5][5]);
}
Python:
import numpy as np
from ctypes import cdll
import ctypes
from numpy.ctypeslib import ndpointer
_p = ndpointer(dtype=np.uint16, ndim=2, shape=(10, 10), flags='C')
mydll = cdll.LoadLibrary("mydll.dll")
_func = mydll.Test
_func.argtypes = [_p]
_func.restypes = ctypes.c_uint16
data = np.empty([10, 10], dtype=np.uint16)
data[5, 5] = 5
print(_func(data))
I get OSError: access violation reading 0xFFFFFFFFFFFFFFFFFFFFFFF what am I doing wrong and how do I fix it?
解决方案
Listing [SciPy.Docs]: C-Types Foreign Function Interface (numpy.ctypeslib) (and [Python 3.Docs]: ctypes - A foreign function library for Python just in case).
This is a exactly like [SO]: Calling C function in Python through ctypes, but function returns incorrect value (@CristiFati's answer) (a duplicate), it just happens to also invlove NumPy.
In other words, you have Undefined Behavior, as argtypes must be CTypes types (not NumPy).
Below is a modified version of the your code, that works.
dll00.c:
#include <stdint.h>
#if defined(_WIN32)
# define DLL00_EXPORT_API __declspec(dllexport)
#else
# define DLL00_EXPORT_API
#endif
#if defined(__cplusplus)
extern "C" {
#endif
DLL00_EXPORT_API uint16_t dll00Func00(uint16_t **ppArr);
#if defined(__cplusplus)
}
#endif
uint16_t dll00Func00(uint16_t **ppArr) {
return ppArr[5][5];
}
code00.py:
#!/usr/bin/env python3
import sys
import ctypes as ct
import numpy as np
DLL_NAME = "./dll00.dll"
def main():
UI16Ptr = ct.POINTER(ct.c_uint16)
UI16PtrPtr = ct.POINTER(UI16Ptr)
dll00 = ct.CDLL(DLL_NAME)
dll00Func00 = dll00.dll00Func00
dll00Func00.argtypes = [UI16PtrPtr]
dll00Func00.restype = ct.c_uint16
dim0 = 10
dim1 = 10
np_arr_2d = np.empty([dim0, dim1], dtype=np.uint16)
np_arr_2d[5][5] = 5
print(np_arr_2d)
# The "magic" happens in the following (3) lines of code
ct_arr = np.ctypeslib.as_ctypes(np_arr_2d)
UI16PtrArr = UI16Ptr * ct_arr._length_
ct_ptr = ct.cast(UI16PtrArr(*(ct.cast(row, UI16Ptr) for row in ct_arr)), UI16PtrPtr)
res = dll00Func00(ct_ptr)
print("\n{0:s} returned: {1:d}".format(dll00Func00.__name__, res))
if __name__ == "__main__":
print("Python {0:s} {1:d}bit on {2:s}\n".format(" ".join(item.strip() for item in sys.version.split("\n")), 64 if sys.maxsize > 0x100000000 else 32, sys.platform))
print("NumPy: {0:s}\n".format(np.version.version))
main()
print("\nDone.")
Output:
[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q058727931]> sopr.bat *** Set shorter prompt to better fit when pasted in StackOverflow (or other) pages *** [prompt]> "c:\Install\x86\Microsoft\Visual Studio Community\2017\VC\Auxiliary\Build\vcvarsall.bat" x64 ********************************************************************** ** Visual Studio 2017 Developer Command Prompt v15.9.17 ** Copyright (c) 2017 Microsoft Corporation ********************************************************************** [vcvarsall.bat] Environment initialized for: 'x64' [prompt]> dir /b code00.py dll00.c [prompt]> cl /nologo /DDLL dll00.c /link /NOLOGO /DLL /OUT:dll00.dll dll00.c Creating library dll00.lib and object dll00.exp [prompt]> dir /b code00.py dll00.c dll00.dll dll00.exp dll00.lib dll00.obj [prompt]> "e:\Work\Dev\VEnvs\py_064_03.07.03_test0\Scripts\python.exe" code00.py Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] 64bit on win32 NumPy: 1.16.2 [[19760 5277 632 0 32464 5280 632 0 111 114] [ 107 92 68 101 118 92 86 69 110 118] [ 115 92 112 121 95 48 54 52 95 48] [ 51 46 48 55 46 48 51 95 116 101] [ 115 116 48 92 108 105 98 92 115 105] [ 116 101 45 112 97 5 107 97 103 101] [ 115 92 110 117 109 112 121 92 116 101] [ 115 116 105 110 103 92 95 112 114 105] [ 118 97 116 101 92 110 111 115 101 116] [ 101 115 116 101 114 46 112 121 0 0]] dll00Func00 returned: 5 Done.
The explanation for all those funky conversions can be found at [SO]: C++ & Python: Pass and return a 2D double pointer array from python to c++ (@CristiFati's answer) (and the referenced [SO]: Problems with passing and getting arrays for a C function using ctypes (@CristiFati's answer)).
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