4

我有一个 Locker 类型的小型模板类，包含在我想存储在 std::map 中的 boost::intrusive_ptr 中：

template <typename T>
bool LockerManager<T>::
  AddData(const std::string& id, T* pData)
{

  boost::intrusive_ptr<Locker<T> > lPtr(Locker<T>(pData)); // Line 359 - compiles

  mMap.insert(make_pair(id, lPtr));  // Line 361 - gives error
}

Locker 只是一个容器类；它的构造函数看起来像：

template <typename T>
Locker<T>::
  Locker(T* pData)
  : IntrusivePtrCountable(),
    mpData(pData),
    mThreadId(0),
    mDataRefCount(0)
{}

在我对这门课的测试中，我正在尝试执行以下操作：

class Clayton
{
public:
  static int count;

  Clayton()
  { mNumber = count++;}

  void GetNumber()
  { cerr<<"My number is: "<<mNumber<<endl; }

private:
  int mNumber;
};

int Clayton::count = 0;

class ClaytonManager
{
public:
  bool AddData(const std::string& id, Clayton* pData)
  { return mManager.AddData(id, pData); }

private:
  LockerManager<Clayton> mManager;
};

我收到以下编译错误：

Compiling LockerManagerTest.cpp                             : /usr/local/lib/gcc/i686-pc-linux-gnu/3.4.6/../../../../include/c++/3.4.6/bits/stl_pair.h: In constructor `std::pair<_T1, _T2>::pair(const std::pair<_U1, _U2>&) [with _U1 = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _U2 = boost::intrusive_ptr<Locker<Clayton> > (*)(Locker<Clayton>), _T1 = const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _T2 = boost::intrusive_ptr<Locker<Clayton> >]':
../Utilities/include/LockerManager.h:361:   instantiated from `bool LockerManager<T>::AddData(const std::string&, T*) [with T = Clayton]'
src/LockerManagerTest.cpp:35:   instantiated from here
/usr/local/lib/gcc/i686-pc-linux-gnu/3.4.6/../../../../include/c++/3.4.6/bits/stl_pair.h:90: error: no matching function for call to `boost::intrusive_ptr<Locker<Clayton> >::intrusive_ptr(boost::intrusive_ptr<Locker<Clayton> > (* const&)(Locker<Clayton>))'
/usr/local/boost-1.36.0/include/boost-1_36/boost/intrusive_ptr.hpp:94: note: candidates are: boost::intrusive_ptr<T>::intrusive_ptr(const boost::intrusive_ptr<T>&) [with T = Locker<Clayton>]
/usr/local/boost-1.36.0/include/boost-1_36/boost/intrusive_ptr.hpp:70: note:                 boost::intrusive_ptr<T>::intrusive_ptr(T*, bool) [with T = Locker<Clayton>]
/usr/local/boost-1.36.0/include/boost-1_36/boost/intrusive_ptr.hpp:66: note:                 boost::intrusive_ptr<T>::intrusive_ptr() [with T = Locker<Clayton>]
Command exited with non-zero status 1
0:05.40

请帮忙

4

2 回答 2

2

Actually, intrusive_ptr already has a < operator and a copy constructor defined, so that wasn't the problem.

There were two main things that we were missing. First, we needed to use value_type, instead of make_pair, to avoid implicit type conversion in the insert statement. Second, we missed the fact that the intrusive_ptr constructor takes a pointer to the type that it is templated around.

So, the final, working method looks like this:

// ---------------------------------------------------------------------------
// LockerManager::AddData
// ---------------------------------------------------------------------------
template <typename T>
bool LockerManager<T>::
  AddData(const std::string& id, T* pData)
{
  Lock<MutualExclusion> lLock(mMutex);

  if ((pData == NULL) || (mMap.find(id) != mMap.end()))
    return false;

  mMap.insert(typename std::map<std::string, boost::intrusive_ptr<Locker<T> > >::value_type(id, new Locker<T>(pData)));

  return true;
} // LockerManager::AddData
于 2009-04-13T17:03:05.810 回答
1

编译器正在尽最大努力在这里提供帮助。您需要定义具有以下签名的方法：

boost::intrusive_ptr<Locker<Clayton> >::intrusive_ptr(
    boost::intrusive_ptr<Locker<Clayton> > (* const&)(Locker<Clayton>)
):

您需要为存储在 std::map 中的类型定义一个复制构造函数，这就是此错误消息试图传达的内容。您还应该实现 < 运算符，以便满足以下条件：

- ( x < x ) == false
- if ( x < y ), then !( y < x )
- if ( x == y ), then ( x < y ) == ( y < x ) == false
- if ( x < y ) and ( y < z ), then ( x < z )

对于许多内置类型，C++ 将为您提供这些，这就是为什么有些人不知道如何将自定义对象存储在 std::map 和其他 STL 容器中。

于 2009-04-12T00:01:48.770 回答