We will use a simplified version of the message library presented in previous chapters. The source tree is organized as follows:

.
├── cmake
│   └── UseDoxygenDoc.cmake
├── CMakeLists.txt
├── docs
│   ├── Doxyfile.in
│   └── front_page.md
└── src
    ├── CMakeLists.txt
    ├── hello-world.cpp
    ├── Message.cpp
    └── Message.hpp

We still have our sources under the src subdirectory, and we have custom CMake modules in the cmake subdirectory. Since our emphasis is on the documentation, we have removed the dependency on UUID and simplified the source code. The most significant differences are the numerous code comments in the header file:

#pragma once

#include <iosfwd>
#include <string>

/*! \file Message.hpp */

/*! \class Message
 * \brief Forwards string to screen
 * \author Roberto Di Remigio
 * \date 2018
 */
class Message {
public:
  /*! \brief Constructor from a string
   * \param[in] m a message
   */
  Message(const std::string &m) : message_(m) {}
  /*! \brief Constructor from a character array
   * \param[in] m a message
   */
  Message(const char *m) : message_(std::string(m)) {}

  friend std::ostream &operator<<(std::ostream &os, Message &obj) {
    return obj.printObject(os);
  }

private:
  /*! The message to be forwarded to screen */
  std::string message_;
  /*! \brief Function to forward message to screen
   * \param[in, out] os output stream
   */
  std::ostream &printObject(std::ostream &os);
};

These comments are in the format /*! */, and include some special tags, which are understood by Doxygen (see http://www.stack.nl/~dimitri/doxygen/manual/docblocks.html).