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  1. #include <iostream>
  2. #include <array>
  3. #include <functional>
  4. #include <algorithm>
  5.  
  6. class formatting_streambuf: public std::streambuf
  7. {
  8.    typedef std::function<std::string(const std::string&)> formatter_t;
  9. public:
  10.    formatting_streambuf(std::streambuf* buf, const formatter_t& formatter) : buffer_{}, buf_(buf), formatter_(formatter)
  11.    {
  12.       setp(buffer_.begin(), buffer_.end() - 1);
  13.    }
  14. protected:
  15.    virtual int overflow(int_type c = traits_type::eof()) override
  16.    {
  17.       *pptr() = traits_type::to_char_type(c);
  18.       format();
  19.       return traits_type::not_eof(c);
  20.    }
  21.  
  22.    virtual int sync() override
  23.    {
  24.       format();
  25.       return 0;
  26.    }
  27. private:
  28.    void format()
  29.    {
  30.       const std::string value(buffer_.begin(), pptr() - buffer_.begin());
  31.       const std::string formatted = formatter_(value);
  32.       buf_->sputn(formatted.c_str(), formatted.size());
  33.       setp(buffer_.begin(), buffer_.end());
  34.    }
  35.  
  36.    std::array<char, 1024> buffer_;
  37.    std::streambuf* buf_;
  38.    formatter_t formatter_;
  39. };
  40.  
  41. class formatting_ostream : public std::ostream
  42. {
  43.    typedef std::function<std::string(const std::string&)> formatter_t;
  44. public:
  45.    formatting_ostream(std::ostream& stream, const formatter_t& formatter) : 
  46.       stream_(stream), old_buf_(stream_.rdbuf()), streambuf_(old_buf_, formatter)
  47.    {
  48.       init(&streambuf_);
  49.    }
  50. private:
  51.    std::ostream& stream_;
  52.    std::streambuf* old_buf_;
  53.    formatting_streambuf streambuf_;
  54. };
  55.  
  56. class source
  57. {
  58. public:
  59.    source(std::ostream& stream) : stream_(stream)
  60.    {
  61.    }
  62.  
  63.    void print()
  64.    {
  65.       stream_ << "HeLlO" << std::endl;
  66.    }
  67. private:
  68.    std::ostream& stream_;
  69. };
  70.  
  71. int main()
  72. {
  73.    auto to_lower = [](const std::string& v) -> std::string
  74.    {
  75.       std::string result;
  76.       std::transform(v.begin(), v.end(), std::back_inserter(result), tolower);
  77.       return result;
  78.    };
  79.    formatting_ostream stream(std::cout, to_lower);
  80.    source s(stream);
  81.    s.print();
  82.    s.print();
  83.  
  84.    source ss(std::cout);
  85.    ss.print();
  86. }
Success #stdin #stdout 0s 3236KB
comments (?)
stdin
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Standard input is empty
stdout
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hello
hello
HeLlO
https://ideone.com/GmOjyf
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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