ceph/src/boost/boost/histogram/detail/counting_streambuf.hpp

   1 // Copyright 2019 Hans Dembinski
   2 //
   3 // Distributed under the Boost Software License, Version 1.0.
   4 // (See accompanying file LICENSE_1_0.txt
   5 // or copy at http://www.boost.org/LICENSE_1_0.txt)
   6
   7 #ifndef BOOST_HISTOGRAM_DETAIL_COUNTING_STREAMBUF_HPP
   8 #define BOOST_HISTOGRAM_DETAIL_COUNTING_STREAMBUF_HPP
   9
  10 #include <boost/core/exchange.hpp>
  11 #include <ostream>
  12 #include <streambuf>
  13
  14 namespace boost {
  15 namespace histogram {
  16 namespace detail {
  17
  18 // detect how many characters will be printed by formatted output
  19 template <class CharT, class Traits = std::char_traits<CharT>>
  20 struct counting_streambuf : std::basic_streambuf<CharT, Traits> {
  21   using base_t = std::basic_streambuf<CharT, Traits>;
  22   using typename base_t::char_type;
  23   using typename base_t::int_type;
  24
  25   std::streamsize* p_count;
  26
  27   counting_streambuf(std::streamsize& c) : p_count(&c) {}
  28
  29   std::streamsize xsputn(const char_type* /* s */, std::streamsize n) override {
  30     *p_count += n;
  31     return n;
  32   }
  33
  34   int_type overflow(int_type ch) override {
  35     ++*p_count;
  36     return ch;
  37   }
  38 };
  39
  40 template <class C, class T>
  41 struct count_guard {
  42   using bos = std::basic_ostream<C, T>;
  43   using bsb = std::basic_streambuf<C, T>;
  44
  45   counting_streambuf<C, T> csb;
  46   bos* p_os;
  47   bsb* p_rdbuf;
  48
  49   count_guard(bos& os, std::streamsize& s) : csb(s), p_os(&os), p_rdbuf(os.rdbuf(&csb)) {}
  50
  51   count_guard(count_guard&& o)
  52       : csb(o.csb), p_os(boost::exchange(o.p_os, nullptr)), p_rdbuf(o.p_rdbuf) {}
  53
  54   count_guard& operator=(count_guard&& o) {
  55     if (this != &o) {
  56       csb = std::move(o.csb);
  57       p_os = boost::exchange(o.p_os, nullptr);
  58       p_rdbuf = o.p_rdbuf;
  59     }
  60     return *this;
  61   }
  62
  63   ~count_guard() {
  64     if (p_os) p_os->rdbuf(p_rdbuf);
  65   }
  66 };
  67
  68 template <class C, class T>
  69 count_guard<C, T> make_count_guard(std::basic_ostream<C, T>& os, std::streamsize& s) {
  70   return {os, s};
  71 }
  72
  73 } // namespace detail
  74 } // namespace histogram
  75 } // namespace boost
  76
  77 #endif