Hi I have problem with CTYPES in python. I have ready dll library with some callback. On swift everything works, but I have some problem in python.
Python:
def set_up_callback(self):
self.lib.set_callback(self.callback1)
@CFUNCTYPE(None, c_float, c_float, c_float, c_uint64)
def callback1( a, b, c, time):
print(a, b, c, time)
c++ declaration of callback
typedef void(*callbackType)(float, float, float, uint64_t, void*);
callbackType callback;
void* context;
c++ init
void setCallback(callbackType callback, void* context) {
this->context = context;
this->callback = callback;
}
c++ induction
callback(1.5f, 2.4f, 1.3f, timestamp, context);
shared.h
extern "C" void SHARED_EXPORT set_callback(callbackType callback, void* context);
and this works good but I would like have self
In callback function so I try this
def set_up_callback(self):
callback_type = CFUNCTYPE(None, c_float, c_float, c_float, c_uint64)
callback = callback_type(self.callback1)
self.lib.set_callback(callback)
def callback1(self, a, b, c, time):
print(a, b, c, time)
and with this try I have error Segmentation fault: 11
Thank you in advance for help
In set_up_callback
, callback
is a local variable that goes out-of-scope after calling self.lib.set_callback(callback)
. You must keep a reference to callback
for the lifetime that it could be called, so store it as a member variable of the class instance.
Working demo:
demo.cpp
#include <time.h>
#include <stdint.h>
#if defined(_WIN32)
# define API __declspec(dllexport)
#else
# define API
#endif
typedef void(*CALLBACK)(float, float, float, uint64_t, void*);
CALLBACK g_callback;
extern "C" {
API void set_callback(CALLBACK callback) {
g_callback = callback;
}
API void demo(void* context) {
if(g_callback)
g_callback(1.5f, 2.4f, 1.3f, time(nullptr), context);
}
}
demo.py
from ctypes import *
from datetime import datetime
CALLBACK = CFUNCTYPE(None,c_float,c_float,c_float,c_uint64,c_void_p)
class Demo:
def __init__(self):
self.lib = CDLL('./demo')
self.lib.set_callback.argtypes = CALLBACK,
self.lib.set_callback.restype = None
self.lib.demo.argtypes = c_void_p,
self.lib.demo.restype = None
self.set_up_callback()
def callback(self,a,b,c,timestamp,context):
print(a,b,c,datetime.fromtimestamp(timestamp),self.context)
def set_up_callback(self):
self.callback = CALLBACK(self.callback)
self.lib.set_callback(self.callback)
def demo(self,context):
self.context = context
self.lib.demo(None)
demo = Demo()
demo.demo([1,2,3])
demo.demo(123.456)
demo.demo('a context')
Output:
1.5 2.4000000953674316 1.2999999523162842 2020-04-11 11:38:44 [1, 2, 3]
1.5 2.4000000953674316 1.2999999523162842 2020-04-11 11:38:44 123.456
1.5 2.4000000953674316 1.2999999523162842 2020-04-11 11:38:44 a context
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.