SFINAE模板錯誤

Question

我使用SFINEA訂閱到ROS通用主題，偵聽每一個主題，並使用SFINEA如果存在返回header.stamp時間。這反序列化的速度更快。唯一的問題是我有一個問題讓我的訂戶設置。我不斷收到以下編譯錯誤：

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); 
} 

Namespace類

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

你傳入boost::shared_ptr<topic_tools::ShapeShifter>類型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); 

而且都使用const裁判爭論而你在它:)

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 
} 
}