一個神祕的編譯錯誤：無法從'const boost :: shared_ptr <T>'轉換爲'const boost :: shared_ptr <T>'

Question

我想保護對用於多線程日誌記錄和boostlog庫的日誌文件的訪問。

我想這個流類

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

用這種方式（text_sink是boostlog對象）：

//... 
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 

，我得到這個神祕的錯誤：cannot convert from 'const boost::shared_ptr<T>' to 'const boost::shared_ptr<T>'

整個編譯錯誤：

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 

我懷疑我沒有很好地定義運營商< <（）...但我不覺得有什麼問題。

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

Answer 1

從錯誤信息presuably pBackend->add_stream，當你給它一個shared_ptr到ThreadSafeStream這是一個完全無關的預期shared_ptr到ostream（！）類型。您需要創建一個超載的add_stream方法，最有可能與ThreadSafeStream一起使用。