CODEWITHSUNDEEP
pythonctypes
user1478497
user1478497

Reputation: 81

Handling struct returned from c++ called from python

I'd like to use a function that is defined in a DLL from Python. The value returned from the C++ function (get_version) is a struct

typedef struct myStruct {
    size_t size;
    char * buff;
} myStruct ;

The Python code is:

lib = CDLL(myDLL.dll)
lib.get_version

The question is how do I handle the returned value?

I've read Voo's answer and reading other posts, but I'm still struggling with this

I declared the struct class (Foo, from Voo's answer) and set the restype The code now looks

class Foo(Structure):
    _fields_ = [('size', c_size_t), ('buff', c_char_p)]

lib = CDLL(myDLL.dll)
lib.get_version
lib.get_version.restype = Foo._fields_

I get the following error TypeError: restype must be a type, a callable, or None

I read about this and if I set the restype not as a list, e.g.: c_char_p, the error doesn't appear

When I set the restype

lib.restype = Foo.fields

The error doesn't appear but the restype for get_version is not set correctly When looking at the variables in debug:

lib.restype = list: [('size', ), ('buff', )]

lib.get_version.restype = PyCSimpleType:

Any help would be appreciated

Upvotes: 3

Views: 1971

Answers (1)

Voo
Voo

Reputation: 30235

You'll have to use the ctypes module. You'll just have to define the struct in your python code with ctypes.

Something like:

>>> from ctypes import *
>>> class Foo(Structure):
...     _fields_ = [("size", c_size_t), ("buff", c_char_p)]

should do the trick. Then you just set the restype of your get_version method to your struct so that the interpreter knows what it does return and then you can use it as expected.

Upvotes: 2

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