ctypes 不允许多次取消引用指针

Question

我一直致力于通过 ctypes 将一些 C++ classes 扩展到 python。我首先尝试通过 GDB 和代码验证地址不等于 NULL。它确实不等于NULL。我尝试通过 printf 打印出指针并打印出地址，但是涉及指针的下一行代码引发了分段错误。奇怪的是，如果没有该 printf 语句，则 printf 语句之后的下一行代码将起作用。然而，下一个涉及指针的函数将抛出一个分段错误，就像 printf 一样。

这是我的代码供参考：

C++->C ctypes 包装器

#include <jetfuelmedia.h>

#define MAX_FILE_NAME_SIZE 1024

extern "C"{
jetfuel::media::Music *Music_new(){
    return new jetfuel::media::Music();
}

void Music_delete(jetfuel::media::Music *music){
    puts("Destroyed Music object");
    delete music;
}

bool Music_is_music_playing(){
    return Mix_PlayingMusic();
}

bool Music_is_music_paused(){
    return Mix_PausedMusic();
}

bool Music_load_music_file(jetfuel::media::Music *music,
                           const wchar_t *musicfilepath){
    char musicfilepathchar[MAX_FILE_NAME_SIZE];

    wcstombs(musicfilepathchar,musicfilepath,
            MAX_FILE_NAME_SIZE);

    puts("Music file is:");
    puts(musicfilepathchar);
    puts("Music ref is:");
    printf("%p",music);

    if(!music->Load_music_file(musicfilepathchar)){
        puts(musicfilepathchar);
        puts(Mix_GetError());
        return false;
    }

    puts("C/C++ code ran");

    return true;
}

bool Music_play(jetfuel::media::Music *music){
    puts("C/C++ Play code ran");
    return music->Play();
}

void Music_pause(jetfuel::media::Music *music){
    music->Pause();
}

void Music_resume(jetfuel::media::Music *music){
    music->Resume();
}

const char *Get_music_error(){
    const char *sdlerror = Mix_GetError();

    if(sdlerror == NULL){
        return "Music object was equal to NULL";
    }
    return Mix_GetError();
}
}

Python class 包装器：

from ctypes import cdll
from ctypes import c_wchar_p
from ctypes import c_void_p
from ctypes import c_bool

class music():  
   _jetfuel = None;
   _musicref = None;

    def __init__(self,jetfuelsofilepath):
        self._jetfuel = cdll.LoadLibrary(jetfuelsofilepath);
        self._musicref = self._jetfuel.Music_new();

    def __enter__(self):
        return self;

    def __exit__(self, exc_type, exc_value, traceback):
        if(self._musicref != None):
            self._jetfuel.Music_delete(c_void_p(self._musicref));

    def is_music_playing(self):
        return self._jetfuel.Music_is_music_playing();

    def is_music_paused(self):
        return self._jetfuel.Music_is_music_paused();

    def load_music_file(self, musicfilepath):
        loadmusicfile = self._jetfuel.Music_load_music_file;
        loadmusicfile.argtypes = [c_void_p, c_wchar_p];
        loadmusicfile.restype = c_bool;

        return loadmusicfile(c_void_p(self._musicref), 
                         c_wchar_p(musicfilepath));

    def play(self):
        return self._jetfuel.Music_play(c_void_p(self._musicref));

    def pause(self):
        self._jetfuel.Music_pause(c_void_p(self._musicref));

    def resume(self):
        self._jetfuel.Music_resume(c_void_p(self._musicref));

    def print_debug(self):
        print("Music ref is ="+str(c_void_p(self._musicref)));

    def get_music_error(self):
        return self._jetfuel.Get_music_error();

如何使此代码与可多次取消引用的指针一起工作？

如果这涉及到任何问题，我的系统信息是：

Ubuntu 17.04 64 位
海湾合作委员会（G++）5.4.1
GDB 7.12.50
Python 3.6
SDL 2.0.3

Answer 1

您忘记设置 restype of Music_new:

def __init__(self,jetfuelsofilepath):
    self._jetfuel = cdll.LoadLibrary(jetfuelsofilepath)
    self._jetfuel.Music_new.restype = c_void_p
    self._musicref = self._jetfuel.Music_new()

默认是int，把指针搞乱了。其他功能将需要类似的处理。为了保持整洁，我建议您在一个地方完成所有这些工作（例如函数 load_jetfuel_library）。

ctypes 不允许多次取消引用指针

ctypes does not allow dereference of pointer more than once

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