一个神秘的编译错误：无法从'const boost :: shared_ptr <T>'转换为'const boost :: shared_ptr <T>'

Question

我想保护对用于多线程日志记录和boostlog库的日志文件的访问。

我想这个流类

class ThreadSafeStream 
{ 
public: 
    template <typename TInput> 
    const ThreadSafeStream& operator<< (const TInput &tInput) const 
    { 
     // some thread safe file access  
     return *this; 
    } 
}; 

用这种方式（text_sink是boostlog对象）：

//... 
m_spSink.reset(new text_sink); 
text_sink::locked_backend_ptr pBackend = m_spSink->locked_backend(); 

const boost::shared_ptr<ThreadSafeStream>& spFileStream = boost::make_shared<ThreadSafeStream>(); 

pBackend->add_stream(spFileStream); // this causes the compilation error 

，我得到这个神秘的错误：cannot convert from 'const boost::shared_ptr<T>' to 'const boost::shared_ptr<T>'

整个编译错误：

Log.cpp(79): error C2664: 'boost::log2_mt_nt5::sinks::basic_text_ostream_backend<CharT>::add_stream' : cannot convert parameter 1 from 'const boost::shared_ptr<T>' to 'const boost::shared_ptr<T> &' 
1>   with 
1>   [ 
1>    CharT=char 
1>   ] 
1>   and 
1>   [ 
1>    T=ThreadSafeStream 
1>   ] 
1>   and 
1>   [ 
1>    T=std::basic_ostream<char,std::char_traits<char>> 
1>   ] 
1>   Reason: cannot convert from 'const boost::shared_ptr<T>' to 'const boost::shared_ptr<T>' 
1>   with 
1>   [ 
1>    T=ThreadSafeStream 
1>   ] 
1>   and 
1>   [ 
1>    T=std::basic_ostream<char,std::char_traits<char>> 
1>   ] 
1>   No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called 

我怀疑我没有很好地定义运营商< <（）...但我不觉得有什么问题。

这是addStream的原型：void add_stream(shared_ptr<stream_type> const& strm);与typedef std::basic_ostream<target_char_type> stream_type;

Answer 1

从错误信息presuably pBackend->add_stream，当你给它一个shared_ptr到ThreadSafeStream这是一个完全无关的预期shared_ptr到ostream（！）类型。您需要创建一个超载的add_stream方法，最有可能与ThreadSafeStream一起使用。