如何在Cython中将指针传递给c函数? [英] How do I pass a pointer to a c function in Cython?
问题描述
我正在尝试使用自定义比较功能在Cython中调用 qsort
,但是我不知道如何传递函数引用。首先,我有一个结构:
I'm trying call qsort
in Cython with a custom compare function but I don't understand how to pass the function reference. First, I have a struct:
cdef struct Pair:
int i,j
float h
比较函数按 h
排序:
cdef int compare(const_void *a, const_void *b):
cdef float v = ((<Pair*>a)).h-((<Pair*>b)).h
if v < 0: return -1
if v > 0: return 1
return 0
这是我遇到的问题:
cdef Pair[5] pa
for i in range(5):
pa[i].i = i;
pa[i].j = i*2;
pa[i].h = i*.5;
qsort(pa,5,sizeof(Pair),compare)
最后一行赢了不会编译并生成此错误,我认为这与以下事实有关:我无法弄清楚如何通过 compare
作为对 qsort的引用
:
The last line won't compile and generates this error which I believe is related to the fact that I can't figure out how to pass compare
as a reference to qsort
:
Cannot assign type 'int (const_void *, const_void *)' to 'int (*)(const_void *, const_void *) nogil'
推荐答案
I无法重现您的错误。您使用的代码是正确的,并且可以与Cython 0.15一起使用。我唯一看到的可能是您的错误是该类型后面附加的 gil。如果要专门将导入的方法声明为 gil safe,请在声明末尾附加 nogil。
I've not been able to reproduce your error. The code you're using is right, and working with Cython 0.15. The only thing i see that might be your error is the "gil" appended to the type. If you want to specifically declare a imported method as "gil safe", append "nogil" at the end of the declaration.
(请注意,您可以检查python代码并用cython -a打开,然后打开Web浏览器)
(note that you can check your python code with cython -a , then open web browser for )
cdef extern from "stdlib.h":
ctypedef void const_void "const void"
void qsort(void *base, int nmemb, int size,
int(*compar)(const_void *, const_void *)) nogil
cdef struct Pair:
int i,j
float h
cdef int compare(const_void *a, const_void *b):
cdef float v = ((a)).h-((b)).h
print 'do something with', v
if v 0: return 1
return 0
def r():
cdef Pair[5] pa
for i in range(5):
pa[i].i = i;
pa[i].j = i*2;
pa[i].h = i*.5;
print 'call qsort'
qsort(pa,5,sizeof(Pair),compare)
print 'call qsort done'
r()
此代码段编译为:
$ cython --version
Cython version 0.15
$ cython --embed test.pyx
$ gcc -I/usr/include/python2.7 -Wall -std=c99 test.c -lpython2.7
$ ./a.out
call qsort
do something with -0.5
do something with -0.5
do something with -0.5
do something with -1.0
do something with -0.5
call qsort done
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