multithread-safe alternative cout/wcout stream (line outputter)

mt_cline.hpp

/*
 * mt_cline.hpp - multithread-safe alternative cout/wcout stream (line outputter)
 *
 * (C) Copyright yohhoy 2015.
 * Distributed under the Boost Software License, Version 1.0.
 * (See copy at http://www.boost.org/LICENSE_1_0.txt)
 */
#include <iostream>
#include <mutex>
#include <string>
#include <utility>

template <typename charT, typename Trait=std::char_traits<charT>>
class mt_lineout {
  using streamT = std::basic_ostream<charT, Trait>;
  static std::mutex& guard() {
    static std::mutex lineout_guard;
    return lineout_guard;
  }
  streamT& os_;
public:
  explicit mt_lineout(streamT& os) : os_(os) {
    guard().lock();
  }
  ~mt_lineout() {
    std::endl(os_);
    guard().unlock();
  }
  mt_lineout(const mt_lineout&) = delete;
  mt_lineout& operator=(const mt_lineout&) = delete;
  mt_lineout(mt_lineout&&) = default;
  mt_lineout& operator=(mt_lineout&) = default;

  template <typename U>
  mt_lineout& operator<<(U&& u) {
    os_ << std::forward<U>(u);
    return *this;
  }
  // feed std::flush/endl/ends
  mt_lineout& operator<<(streamT& (&)(streamT&)) { return *this; }
};

inline mt_lineout<char> cline()
{ return mt_lineout<char>(std::cout); }

inline mt_lineout<wchar_t> wcline()
{ return mt_lineout<wchar_t>(std::wcout); }

When you want to output "line by line" under multi-threaded code,

cline() << "Hello, world: " << 42 << " pi=" << 3.14;