How to write vector of ostreams in C++ which takes in all the different output streams like cout, ostringstream and ofstream

  • A+
Category:Languages

I am trying to implement a logger which can be registered with multiple streams like ostringstream, ofstream etc. I tried to implement the function like this

void register_stream(std::ostream& a); 

The vector is as follows

std::vector<std::ostream> streams; 

The register stream and operator overloading is as follows

void logger::register_stream(std::ostream &a)`  {      streams.push_back(a);  }  template <typename T>  void logger::operator<<(T const& value)  {      for (auto stream : streams)      {          (stream) << value;      }  } 

I am trying to implement a logger to write to all registered streams on a single operator "<<" call.

The following is the invocation code:

std::ostringstream os;     std::ofstream f;     logger l;     l.register_stream(f);     l.register_stream(os);     l << "log this"; 

I am getting an error:

C2280: std::basic_ostream<char,std::char_traits<char>>::basic_ostream(const std::basic_ostream<char,std::char_traits<char>> &): attempting to reference a deleted function

Any help would be much appreciated.

 


You can't store copies of your streams, they are not copiable. You have to store std::reference_wrappers or pointers instead.

class logger {     std::vector<std::reference_wrapper<std::ostream>> streams; public:     void register_stream(std::ostream &stream) {         streams.emplace_back(stream);     }      template <typename T>     void operator<<(T const &value) {         for (auto &stream : streams) { // note the '&'             stream.get() << value;         }     } }; 

or if you want to be able to chain your calls like l << "log" << " this";:

    template <typename T>     logger & operator<<(T const &value) {         for (auto &stream : streams) {             stream.get() << value;         }         return *this;     } 

Comment

:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen: