用于std :: list of boost :: shared_ptr的迭代器问题

Question

我遇到以下代码的问题:

#include <list>
#include <boost/shared_ptr.hpp>
#include "Protocol/IMessage.hpp"

template <typename HeaderType>
class Connection {
 public:
  typedef IMessage<HeaderType>             MessageType;
  typedef boost::shared_ptr<MessageType>   MessagePointer; 

  template <typename Handler>
  void
  FlushMessageQueue(Handler handler) {
    std::list<MessagePointer>::iterator ib = message_queue_.begin(); // line 69
    std::list<MessagePointer>::iterator ie = message_queue_.end();
    for (; ib != ie; ++ib) {
      AsyncWrite(*ib, handler);
    }
  }

 private:
  std::list<MessagePointer> message_queue_;
};

gcc(4.2.1)告诉我:

include/Network/Connection.hpp: In member function 'void Network::Connection<MT>::FlushMessageQueue(Handler)':
include/Network/Connection.hpp:69: error: expected `;' before 'ib'

我想知道为什么我不能为MessagePointer的列表创建一个迭代器.

有任何想法吗？

谢谢.

Answer 1

std::list<MessagePointer>在您的代码中是一个依赖类型(即它取决于模板参数的类型).因此,您需要使用typename以声明::iterator所有潜在实例化的类型(因为它可能是某些实例化的值,如果它们是专门的).所以:

typename std::list<MessagePointer>::iterator ib = message_queue_.begin();