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from libc.stdlib cimport malloc, free
# Example C struct
ctypedef struct my_c_struct:
int a
int b
cdef class WrapperClass:
"""A wrapper class for a C/C++ data structure"""
cdef my_c_struct *_ptr
cdef bint ptr_owner
def __cinit__(self):
self.ptr_owner = False
def __dealloc__(self):
# De-allocate if not null and flag is set
if self._ptr is not NULL and self.ptr_owner is True:
free(self._ptr)
self._ptr = NULL
def __init__(self):
# Prevent accidental instantiation from normal Python code
# since we cannot pass a struct pointer into a Python constructor.
raise TypeError("This class cannot be instantiated directly.")
# Extension class properties
@property
def a(self):
return self._ptr.a if self._ptr is not NULL else None
@property
def b(self):
return self._ptr.b if self._ptr is not NULL else None
@staticmethod
cdef WrapperClass from_ptr(my_c_struct *_ptr, bint owner=False):
"""Factory function to create WrapperClass objects from
given my_c_struct pointer.
Setting ``owner`` flag to ``True`` causes
the extension type to ``free`` the structure pointed to by ``_ptr``
when the wrapper object is deallocated."""
# Fast call to __new__() that bypasses the __init__() constructor.
cdef WrapperClass wrapper = WrapperClass.__new__(WrapperClass)
wrapper._ptr = _ptr
wrapper.ptr_owner = owner
return wrapper
@staticmethod
cdef WrapperClass new_struct():
"""Factory function to create WrapperClass objects with
newly allocated my_c_struct"""
cdef my_c_struct *_ptr = <my_c_struct *>malloc(sizeof(my_c_struct))
if _ptr is NULL:
raise MemoryError
_ptr.a = 0
_ptr.b = 0
return WrapperClass.from_ptr(_ptr, owner=True)
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