c++ - SFINAE 模板错误

Question

我正在使用 SFINEA 订阅 ROS 中的通用主题，它会监听每个主题，并使用 SFINEA 返回 header.stamp 时间(如果存在)。这可以更快地反序列化。唯一的问题是我在设置订户时遇到问题。我不断收到以下编译错误:

CMakeFiles/performance_tracker.dir/src/performance_tracker.cpp.o: 
In function   PerformanceTracker::topicCallback(boost::shared_ptr<topic_tools::ShapeShifter>)
ros/src/performance_tracker/src/performance_tracker.cpp:32:
undefined reference to boost::disable_if<timewarp::has_header<boost::shared_ptr<topic_tools::ShapeShifter> >, ros::Time>::type
timewarp::extractTime<boost::shared_ptr<topic_tools::ShapeShifter> >(boost::shared_ptr<topic_tools::ShapeShifter>)

主要

 // Subscribe To Generic Message 
 _sub =  _nh.subscribe( _topicName, 1, &PerformanceTracker::topicCallback, this);


void PerformanceTracker::topicCallback(const boost::shared_ptr<topic_tools::ShapeShifter> data){
//Current Time
ros::Time begin = ros::Time::now();
ros::Time timePublished = timewarp::extractTime<boost::shared_ptr<topic_tools::ShapeShifter>>(data);
}

命名空间类

namespace timewarp
{
template <typename T>
struct has_header {
    typedef char yes[1];
    typedef char no[2];

    template <typename C>
    static yes& test(typename C::_header_type*);

    template <typename>
    static no& test(...);

    // If the "sizeof" the result of calling test<T>(0) would be equal to the sizeof(yes),
    static const bool value = sizeof(test<T>(0)) == sizeof(yes);
};

template<class MsgType>
typename boost::enable_if<has_header<MsgType>, ros::Time>::type extractTime(const boost::shared_ptr<topic_tools::ShapeShifter> data)
{
    boost::shared_ptr<MsgType> ptr = data->instantiate<MsgType>();
    assert(ptr);

    return ptr->header.stamp;
}

template<class MsgType>
typename boost::disable_if<has_header<MsgType>, ros::Time>::type extractTime(const boost::shared_ptr<topic_tools::ShapeShifter>);

}

Answer 1

您正在传递 boost::shared_ptr<topic_tools::ShapeShifter>类型为 MsgType 到 has_header<T>而不是 topic_tools::ShapeShifter .

我相信你想做的事:

ros::Time timePublished = timewarp::extractTime<topic_tools::ShapeShifter>(data);

并在使用时使用 const refs 参数 :)

template<class MsgType>
typename boost::enable_if<has_header<MsgType>, ros::Time>::type extractTime(const boost::shared_ptr<MsgType>& data)
{
    boost::shared_ptr<MsgType> ptr = data->instantiate<MsgType>();
    assert(ptr);

    return ptr->header.stamp;
}

template<class MsgType>
typename boost::disable_if<has_header<MsgType>, ros::Time>::type extractTime(const boost::shared_ptr<MsgType>&)
{
    return ros::Time::now(); 
    // or whatever ros time you need to return for types without headers
}
}