[英]how to call a c-function expecting a pointer to a structure with ctypes?
I face the following problem.我面临以下问题。 In C I wrote the following:
在 C 我写了以下内容:
#include <stdio.h>
typedef struct {
double *arr;
int length;
} str;
void f(str*);
int main (void){
double x[3] = {0.1,0.2,0.3};
str aa;
aa.length = 3;
aa.arr = x;
f(&aa);
return 0;
}
void f(str *ss){
int i;
printf("%d\n",ss->length);
for (i=0; i<ss->length; i++) {
printf("%e\n",ss->arr[i]);
}
}
If I compile it to an executable it works correctly.如果我将它编译为可执行文件,它可以正常工作。 I receive:
我收到:
3
0.1
0.2
0.3
as it should be.应该是这样。 After building the shared library 'pointertostrucCtypes.so' from the C-code above I call the function f in python as follows:
从上面的 C 代码构建共享库“pointertostrucCtypes.so”后,我在 python 中调用 function f 如下:
ptrToDouble = ctypes.POINTER(ctypes.c_double)
class pystruc (ctypes.Structure):
_fields_=[
("length",ctypes.c_int),
("arr",ptrToDouble)
]
aa = pystruc()
aa.length = ctypes.c_int(4)
xx = numpy.arange(4,dtype=ctypes.c_double)
aa.arr = xx.ctypes.data_as(ptrToDouble)
myfunc = ctypes.CDLL('pointertostrucCtypes.so')
myfunc.f.argtypes = [ctypes.POINTER(pystruc)]
myfunc.f(ctypes.byref(aa))
It results always in printing out an arbitrary integer and afterwards it gives me a segmentation fault.它总是导致打印出任意 integer ,然后它给我一个分段错误。 because length does not fit.
因为长度不合适。 Has somebody an idea what I do wrong here?
有人知道我在这里做错了什么吗?
Your fields are reversed.你的字段被颠倒了。 Try:
尝试:
class pystruc (ctypes.Structure):
_fields_=[
("arr",ptrToDouble)
("length",ctypes.c_int),
]
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