passing structure from c++ to python

Question

C++ code

typedef struct Box
{
   public:
      int length;   // Length of a box
      int breadth;  // Breadth of a box
      int height;   // Height of a box
};

extern "C"
{
    //struct Box __declspec(dllexport) GetAllInfo();
    TESTAPI struct Box * GetAllInfo();
}

extern "C"
{
    TESTAPI struct Box * GetAllInfo()
    {
       Box *Box1 = new Box;
       Box1->height = 5;
       Box1->length = 6;
       Box1->breadth = 7;

       cout << "Info is : " << Box1->height<<Box1->length<<Box1->breadth <<endl;

       return Box1;
   }
}

Python code

import ctypes
from ctypes import Structure, c_int, c_double, windll
from ctypes import *
from ctypes import wintypes
from collections import namedtuple

#astdll = windll.CDll
class Box(object):

    def __init__(self,height,length,breadth):

        self.height = height
        self.length = length
        self.breadth = breadth

#class Box(Structure):

# _fields_ = [

# ("height", ctypes.c_int),
# ("length", ctypes.c_int),
# ("breadth", ctypes.c_int)

# ]

Box = namedtuple("Box", "height length breadth")

lib = cdll.LoadLibrary("F:\\QT SCADA\\forPythonDLL\\Neha_Test\\Debug\\Neha_Test.dll")

#lib.GetAllInfo.restype = POINTER(Box)

s = Box

global result

result = lib.GetAllInfo()

#s = result
s.height = 20

print (result.height)
print (s.height)

This is the error:

Running script: "C:\Users\Administrator\Desktop\test.py"

Info is : 567

Traceback (most recent call last):

File "C:\Users\Administrator\Desktop\test.py", line 41, in

print (result.height)

AttributeError: 'int' object has no attribute 'height'

this is pretty illegible. please see this help which explains how to format your code — scytale
– scytale, Commented Aug 20, 2015 at 16:59

kurtzmarc · Accepted Answer · 2019-07-31 15:10:26Z

2

Thanks fr all the help....:)

I got this code

its working fine

import ctypes
from ctypes import Structure, c_int, c_double, windll
from ctypes import *
from ctypes import wintypes
from collections import namedtuple


lib = cdll.LoadLibrary(DLL_PATH)

class Box(Structure):
_fields_ = [
    ("length", c_int),
    ("breadth", c_int),
    ("height", c_int)]

 lib.GetAllInfo.restype = POINTER(Box)
result = lib.GetAllInfo()
print ("result type: ", type(result))
print ("-"*30)
print ("result: ",result)
print ("-"*30)
print (result.contents)

Box1=result[0]
print(Box1.height)

edited Jul 31, 2019 at 15:10

kurtzmarc

3,1671 gold badge27 silver badges41 bronze badges

answered Aug 21, 2015 at 5:13

nmahale.10

311 silver badge5 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

bawjensen · Accepted Answer · 2015-08-20 17:27:37Z

0

Not 100% sure on this, but at a guess I'd say your issues lies in the fact that the C++ code for GetAllInfo returns a Box pointer (type Box*), which is effectively just an integer referring to a location in memory. You're then trying to get the height attribute of this integer pointer, which is resulting in the error AttributeError: 'int' object has no attribute 'height'.

Try returning a Box object (as below), not a Box pointer, and see if that fixes it.

TESTAPI struct Box * GetAllInfo()
{
   Box *Box1 = new Box;
   Box1->height = 5;
   Box1->length = 6;
   Box1->breadth = 7;

   cout << "Info is : " << Box1->height<<Box1->length<<Box1->breadth <<endl;

   return Box1;
}

becomes

TESTAPI struct Box GetAllInfo()
{
   Box *Box1 = new Box;
   Box1->height = 5;
   Box1->length = 6;
   Box1->breadth = 7;

   cout << "Info is : " << Box1->height<<Box1->length<<Box1->breadth <<endl;

   return (*Box1);
}

answered Aug 20, 2015 at 17:27

bawjensen

1289 bronze badges

1 Comment

J.J. Hakala Over a year ago

That is not a good idea since it creates a memory leak, Box1 is not deallocated since there is no corresponding delete.

Tim · Accepted Answer · 2016-07-24 12:09:49Z

0

You are mixing C and C++. Your updated code works because ctypes.Structure fixes this issue for you. You need to also release the memory you allocate. How you do this depends on what your program needs to do with a Box. One possibility is to use an in/out parameter in GetAllInfo (implementation left as an exercise for the reader).

struct Box {
    int length;   // Length of a box
    int breadth;  // Breadth of a box
    int height;   // Height of a box
};

extern "C" TESTAPI Box* GetAllInfo() {
    Box *Box1 = new Box;
    Box1->height = 5;
    Box1->length = 6;
    Box1->breadth = 7;

    cout << "Info is : " << Box1->height << Box1->length << Box1->breadth << endl;
    return Box1;
}

answered Jul 24, 2016 at 12:09

Tim

1,5371 gold badge9 silver badges16 bronze badges

Collectives™ on Stack Overflow

passing structure from c++ to python

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related