提高:: Python和设置::擦除 - ＆GT;怪异的行为 [英] boost::python and set::erase -> weird behaviour

问题描述

我想存储在一个std ::对象设置。这些对象的boost :: shared_ptr的＆LT;>，从Python环境的到来。添加值的集合不会造成任何麻烦。但是，当我试图抹掉一个值，即使我通过了非常相同的参考，它不会工作。下面是一个例子：

I'm trying to store objects in a std::set. Those objects are boost::shared_ptr<>, coming from the python environment. adding values to the set won't cause any troubles. But when I try to erase a value, even though I'm passing the very same reference, it won't work. Here is an example :

#include <set>
#include <iostream>

#include <boost/shared_ptr.hpp>
#include <boost/python.hpp>

using namespace std;
using namespace boost;
using namespace boost::python;

struct Bar
{
    Bar() {}
};

struct Foo
{
    set< shared_ptr<Bar> > v_set;
    shared_ptr<Bar> v_ptr;

    Foo() {}

    void add( shared_ptr<Bar> v_param ) {
    cout << "storing " << v_param << "in v_set and v_ptr" << endl;
    v_set.insert(v_param);
    v_ptr = v_param;

    }

    void del( shared_ptr<Bar> v_param ) {
    cout << "deleting " << v_param << endl;
    if (v_param == v_ptr) {
        cout << "v_param == v_ptr" << endl;
    } else {
        cout << "v_param != v_ptr" << endl;
    }

    cout << "erasing from v_set using v_param" << endl;
    if (v_set.erase(v_param) == 0) {
        cout << "didn't erase anything" << endl;
    } else {
        cout << "erased !" << endl;
    }

    cout << "erasing from v_set using v_ptr" << endl;
    if (v_set.erase(v_ptr) == 0) {
        cout << "didn't erase anything" << endl;
    } else {
        cout << "erased !" << endl;
    }
    }
};

BOOST_PYTHON_MODULE (test)
{
    class_< Foo, shared_ptr<Foo> >("Foo")
        .def("add",&Foo::add)
        .def("remove",&Foo::del);

    class_< Bar, shared_ptr<Bar> >("Bar");    
}

编译：

%> gcc -pthread -fno-strict-aliasing -march=i686 -mtune=generic -O2 -pipe -DNDEBUG -march=i686 -mtune=generic -O2 -pipe -fPIC -I/usr/include/python2.7 -c test.cpp -o test.o

%> g++ -pthread -shared -Wl,--hash-style=gnu -Wl,--as-needed build/temp.linux-i686-2.7/test.o -L/usr/lib -lboost_python -lpython2.7 -o test.so

现在，小python脚本：

and now, a small python script :

from test import *

f = Foo()
b = Bar()

f.add(b)

f.remove(b)

下面是结果：

storing 0x8c8bc58in v_set and v_ptr
deleting 0x8c8bc58
v_param == v_ptr
erasing from v_set using v_param
didn't erase anything
erasing from v_set using v_ptr
erased !

• 我店0x8e89c58设置内，外，以防万一


• 我传球同样提到两个电话（0x8e89c58）


• 公正，以确保我检查如果v == VAL


• 我尝试使用v到擦除 - 它不工作


• 我尝试使用VAL擦除 - 它的工作原理



我完全失去了那里 - 看不出是什么原因造成这一点。任何输入？

I'm completely lost there - can't see what is causing this. Any input ?

推荐答案

我跑你的榜样，加入了一些说法，我认为应该在持有德尔（）：

I ran your example then added some assertions that I thought should hold in del():

assert(!(v_param < v_ptr));
assert(!(v_ptr < v_param));

他们中的一个失败！

One of them failed!

我挖成的实施运营商的LT; 为的boost :: shared_ptr的并发现了一些奇怪的：它比较引用计数，而不是内部的指针！有一点点找到关于此问题的邮件列表后，提供一些有用的链接两个C ++文件：N1590这也解释了为什么人们认为这是一个好主意，N2637这就解释了为什么它不是

I dug into the implementation of operator< for boost::shared_ptr and found something strange: it compares the reference counts rather than the internal pointers! A little digging found a mailing list post about this issue with some helpful links to two C++ documents: N1590 which explains why people thought this was a good idea, and N2637 which explains why it wasn't.

看来，升压人没有（没有？）通过了N2637的建议，但C ++ 11。于是我重新建造你的测试使用C ++ 11（ G ++ -std =的C ++ 0x ），在除去使用空间boost; ，以便使用的std :: shared_ptr的。这导致其在顶部添加此解决一个可怕的模板缠身的错误信息（容易源自升压/ smart_ptr / shared_ptr.hpp ）

It seems that the Boost people have not (yet?) adopted the N2637 recommendation, but C++11 has. So I built your test again using C++11 (g++ -std=c++0x), having removed using namespace boost; so as to use std::shared_ptr. This resulted in a horrible template-ridden error message which was solved by adding this at the top (easily derived from boost/smart_ptr/shared_ptr.hpp):

template<class T> inline T * get_pointer(std::shared_ptr<T> const & p)
{
    return p.get();
}

和它的作品！

如果您不能使用C ++ 11，只需要实现自己的自定义比较你的一套指针三立比较：

If you can't use C++11, just implement your own custom comparator for your set which compares the pointers sanely:

template <typename T>
struct SmartComparator
{
    bool operator()(shared_ptr<T> const& lhs, shared_ptr<T> const& rhs) {
        return lhs.get() < rhs.get();
    }
};

那么这将工作：

set< shared_ptr<Bar>, SmartComparator<Bar> > v_set;

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