传递一个numpy的指针(DTYPE = np.bool),以C ++ [英] Passing a numpy pointer (dtype=np.bool) to C++
问题描述
我想用通过用Cython传递它的指针要在C型布尔++的numpy的数组。我已经知道如何与其它数据类型一样UINT8做到这一点。这样做与布尔以同样的方式这是行不通的。我能够编译但在运行时出现以下异常:
I'd like to use a numpy array of type bool in C++ by passing its pointer via Cython. I already know how to do it with other datatypes like uint8. Doing it the same way with boolean it does not work. I am able to compile but there is the following Exception during runtime:
Traceback (most recent call last):
File "test.py", line 15, in <module>
c = r.count(b, 4)
File "rect.pyx", line 41, in rect.PyRectangle.count (rect.cpp:1865)
def count(self, np.ndarray[bool, ndim=1, mode="c"] array not None, int size):
ValueError: Does not understand character buffer dtype format string ('?')
下面是我的C ++方法:
Here is my c++ method:
void Rectangle::count(bool * array, int size)
{
for (int i = 0; i < size; i++){
std::cout << array[i] << std::endl;
}
}
在用Cython文件:
The Cython file:
# distutils: language = c++
# distutils: sources = Rectangle.cpp
import numpy as np
cimport numpy as np
from libcpp cimport bool
cdef extern from "Rectangle.h" namespace "shapes":
cdef cppclass Rectangle:
Rectangle(int, int, int, int) except +
int x0, y0, x1, y1
void count(bool*, int)
cdef class PyRectangle:
cdef Rectangle *thisptr # hold a C++ instance which we're wrapping
def __cinit__(self, int x0, int y0, int x1, int y1):
self.thisptr = new Rectangle(x0, y0, x1, y1)
def __dealloc__(self):
del self.thisptr
def count(self, np.ndarray[bool, ndim=1, mode="c"] array not None, int size):
self.thisptr.count(&array[0], size)
和这里的python脚本调用该方法,并产生错误:
And here the python script that calls the method and produces the error:
import numpy as np
import rect
b = np.array([True, False, False, True])
c = r.count(b, 4)
请让我知道如果你需要更多的信息。谢谢!
Please let me know if you need more information. Thank you!
推荐答案
它看起来像问题是与数组类型声明。
据当时 https://cython.readthedocs.org/en/文档最新/ src目录/教程/ numpy.html 布尔一阳还不支持,但是你可以通过铸造他们为无符号的八位整数数组使用它们。
下面是一个简单的例子,需要布尔值的一维数组的总和(同为和()
方法会为一个布尔numpy的数组)
It looks like the problem is with the array type declaration.
According to the documentation at https://cython.readthedocs.org/en/latest/src/tutorial/numpy.html boolean arays aren't yet supported, but you can use them by casting them as arrays of unsigned eight bit integers.
Here's a simple example that takes the sum of a 1D array of boolean values (the same as the sum()
method would for a boolean NumPy array)
from numpy cimport ndarray as ar
cimport numpy as np
cimport cython
@cython.boundscheck(False)
@cython.wraparound(False)
def cysum(ar[np.uint8_t,cast=True] A):
cdef int i, n=A.size, tot=0
for i in xrange(n):
tot += A[i]
return tot
在你的C ++ code,这取决于你在做什么,你可能需要转换指针回一个布尔值,我不知道这一点。
In your C++ code, depending on what you are doing, you may need to cast the pointer back to a bool, I'm not sure on that.
编辑:这里有一个如何转换指针在用Cython,这应该做你想做的一个例子。
我仍然需要数组类型为无符号的8位整数,但后来我投的指针回一个布尔值。
here's an example of how to cast the pointer in Cython, which should do what you want. I still had to type the array as an unsigned 8 bit integer, but I then cast the pointer back into a bool.
from numpy cimport ndarray as ar
cimport numpy as np
from libcpp cimport bool
cimport cython
def cysum(ar[np.uint8_t,cast=True] A):
cdef int i, n=A.size, tot=0
cdef bool *bptr
bptr = <bool*> &A[0]
for i in xrange(n):
tot += bptr[i]
return tot
如果你想传递数组中的指针,你可以只使用下面的函数在用Cython文件:
If you want to pass the array in as a pointer, you could just use the following function in your Cython file:
cdef bool* arptr(np.uint8_t* uintptr):
cdef bool *bptr
bptr = <bool*> uintptr
return bptr
这可以被称为
arptr(&A[0])
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