python ctypes-传递numpy数组-奇数输出 [英] python ctypes - passing numpy array - odd output

问题描述

我正在使用ctypes，并且正在将ndarray传递给c函数. 它给了我奇怪的输出行为. 这是一些代码:

I'm using ctypes and I'm passing a ndarray to a c-function. It gives me a odd output behavior. Heres some code:

C函数:

int foo(int * foo,int N){
for(int i=0;i<N;i++){
    cout << "i " << i  << " "<< foo[i]  << endl;
    }
return 0;
}

Python:

from ctypes import *
import numpy as np
bar = cdll.LoadLibrary(".../libtest.so")
N = c_int(10)
check = np.ones(10, dtype=int)
print check
bar.foo(c_int(check.ctypes.data),N)

输出:

[1 1 1 1 1 1 1 1 1 1]
i:0 out:1
i:1 out:0
i:2 out:1
i:3 out:0
i:4 out:1
i:5 out:0
i:6 out:1
i:7 out:0
i:8 out:1
i:9 out:0

应该没事吗? :)

我正在编译

g++ -g -c -fPIC -O0  pythagoras.cpp 
g++ -shared -Wl,-soname=libtest.so -o libtest.so  pythagoras.o 

有人有什么想法吗?我现在正在搜索故障至少1个小时，而且我不知道解决方案是什么(可能有些愚蠢)

Anyone any ideas? I'm searching the failure now for at least 1hr and I'm having no idea what the solution is(probably something stupid)

提前谢谢！

推荐答案

将dtype设置为Python int将使用C long.如果您使用的是64位平台(而不是Windows)，则为64位数据类型，它解释了交错的0.您可以通过设置dtype=np.int32与dtype=np.int64进行检查.

Setting the dtype to a Python int will use a C long. If you're on a 64-bit platform (other than Windows), that's a 64-bit data type, which explains the interleaved 0s. You can check this by setting dtype=np.int32 vs dtype=np.int64.

第二，check.ctypes.data是表示C void *指针的Python int.将其作为c_int传递是不正确的.至少使用c_void_p，然后定义argtypes:

Secondly, check.ctypes.data is a Python int representing a C void * pointer. Passing it as c_int isn't correct. At a minimum, use c_void_p, and define argtypes:

from ctypes import *
import numpy as np

bar = CDLL('.../libtest.so')
bar.foo.argtypes = [c_void_p, c_int]

check.ctypes定义_as_parameter_ ctypes挂钩，该挂钩返回c_void_p的实例:

check.ctypes defines the _as_parameter_ ctypes hook, which returns an instance of c_void_p:

N = 10
check = np.ones(N, dtype=np.int32)
print check
bar.foo(check.ctypes, N)

您可以使用check.ctypes.data_as或通过使用np.ctypeslib.ndpointer定义类型来更具体.

You can be more specific with check.ctypes.data_as, or by defining a type with np.ctypeslib.ndpointer.

顺便说一句，foo是C ++函数，而不是C.您必须使用extern "C".否则，将破坏导出的名称.

By the way, foo is a C++ function, not C. You must have used extern "C". Otherwise the exported name would be mangled.

这篇关于python ctypes-传递numpy数组-奇数输出的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！