### CPU Timer Constructor (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Constructs a `cpu_timer` object and immediately calls the `start()` method to begin measuring elapsed time. This ensures the timer is active upon instantiation.

```cpp
cpu_timer() noexcept;
```

--------------------------------

### CPU Timer Action: start() (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Begins or resumes the accumulation of elapsed time within the `cpu_timer`. This method records the current time and starts measuring from this point. The timer is active after this call (`!is_stopped()`).

```cpp
void start() noexcept;
```

--------------------------------

### Progress Display Usage Example (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/original_timer

Demonstrates how to use the progress_display class to show progress during a lengthy computation on a std::map. It initializes progress_display with the size of the map and increments it within the loop.

```cpp
  progress_display show_progress( big_map.size() );
  for ( big_map_t::iterator itr = big_map:begin();
        itr != big_map.end(); ++itr )
  {
     // do the computation
     ...
     ++show_progress;
  }
```

--------------------------------

### Using auto_cpu_timer in C++

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Demonstrates the basic usage of `boost::timer::auto_cpu_timer` to measure the elapsed time of a code block. The timer automatically starts upon object creation and reports results upon destruction. This is useful for quick profiling of function or loop execution times.

```cpp
#include <boost/timer/timer.hpp>
#include <cmath>

int main()
{
  boost::timer::auto_cpu_timer t;

  for (long i = 0; i < 100000000; ++i)
    std::sqrt(123.456L); // burn some time

  return 0;
}
```

--------------------------------

### CPU Timer Class Synopsis (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Defines the `cpu_timer` class, which measures wall clock and process elapsed time. It includes methods for starting, stopping, resuming, and querying the elapsed time, as well as formatting the results. It manages internal state to track time accumulation.

```cpp
class cpu_timer
{
public:
  cpu_timer() noexcept;
  ~cpu_timer() noexcept = default;
  cpu_timer(const cpu_timer&) noexcept = default;
  cpu_timer& operator=(const cpu_timer&) noexcept = default;

  bool is_stopped() const noexcept;
  cpu_times elapsed() const noexcept;
  std::string format(int places, const std::string& format) const;
  std::string format(int places = default_places) const;

  void start() noexcept;
  void stop() noexcept;
  void resume() noexcept;
};
```

--------------------------------

### CPU Timer Observer: format() (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Formats the current elapsed time using the `boost::timer::format` non-member function. Allows specifying the number of decimal places and a custom format string. It internally calls `elapsed()` to get the time values.

```cpp
std::string format(int places, const std::string& format) const;
std::string format(int places = default_places) const;
```

--------------------------------

### CPU Timer Observer: elapsed() (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Retrieves the accumulated elapsed time from the `cpu_timer`. If the timer is stopped, it returns the total time recorded up to the last `stop()` call. If the timer is running, it returns the time accumulated since the last `start()` or `resume()` call.

```cpp
cpu_times elapsed() const noexcept;
```

--------------------------------

### Measure Wall-Clock Time Resolution (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/test/cpu_timer_info

Measures the resolution of boost::timer::cpu_timer for wall-clock time. It repeatedly starts the timer, records the elapsed wall-clock time, and continues to measure until the wall-clock time changes, printing the difference in nanoseconds. This is useful for understanding the timer's precision for measuring real-world elapsed time.

```cpp
#include <boost/timer/timer.hpp>
#include <boost/detail/lightweight_main.hpp>
#include <cstdlib> // for atol()
#include <iostream>
#include <locale>

using boost::timer::nanosecond_type;
using boost::timer::cpu_times;
using boost::timer::cpu_timer;
using boost::timer::auto_cpu_timer;
using std::cout; using std::endl;

int cpp_main( int argc, char * argv[] )
{
  cpu_times start_time;
  start_time.clear();
  cpu_times current_time;

  // ... previous code ...
 
  {
    cpu_timer cpu;
    cout << "measure boost::timer::cpu_timer resolution for wall-clock time..." << std::endl;
    for (int i = 0; i < 100; ++i)
    {
      cpu.start();
      start_time.wall = cpu.elapsed().wall;
      current_time.wall = start_time.wall;
      while (current_time.wall == start_time.wall)
      {
        current_time.wall = cpu.elapsed().wall;
      }
      cout << current_time.wall - start_time.wall << "ns ";
    }
  }
 return 0;
}
```

--------------------------------

### Measure CPU Timer Resolution (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/test/cpu_timer_info

Measures the resolution of boost::timer::cpu_timer for user CPU time. It repeatedly starts the timer, records the elapsed user time, and continues to measure until the user time changes, printing the difference in nanoseconds. This helps determine the timer's precision for CPU-bound operations.

```cpp
#include <boost/timer/timer.hpp>
#include <boost/detail/lightweight_main.hpp>
#include <cstdlib> // for atol()
#include <iostream>
#include <locale>

using boost::timer::nanosecond_type;
using boost::timer::cpu_times;
using boost::timer::cpu_timer;
using boost::timer::auto_cpu_timer;
using std::cout; using std::endl;

int cpp_main( int argc, char * argv[] )
{
  cpu_times start_time;
  start_time.clear();
  cpu_times current_time;

  {
    cpu_timer cpu;
    cout << "measure boost::timer::cpu_timer resolution for user time..." << std::endl;
    for (int i = 0; i < 3; ++i)
    {
      cpu.start();
      start_time = cpu.elapsed();
      current_time.user = start_time.user;
      while (current_time.user == start_time.user)
      {
        current_time = cpu.elapsed();
      }
      cout << current_time.user - start_time.user << "ns\n";
    }
  }
 
  // ... rest of the code ...
 return 0;
}
```

--------------------------------

### Boost Timer Library Synopsis

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

This is the synopsis for the Boost Timer library, outlining the main classes and types available. It includes `cpu_timer` for wall clock, user, and system timings, and `auto_cpu_timer` for automatic reporting on destruction. It also defines `nanosecond_type` and the `cpu_times` struct.

```c++
namespace boost
{
  namespace timer
  {
    class cpu_timer;       // wall clock, user, and system timer
    class auto_cpu_timer;  // automatic report() on destruction 

    typedef boost::int_least64_t nanosecond_type;

    struct cpu_times
    {
      nanosecond_type wall;
      nanosecond_type user;
      nanosecond_type system;

      void clear();
    };
      
    const int           default_places = 6;

    std::string format(const cpu_times& times, short places, const std::string& format);
    std::string format(const cpu_times& times, short places = default_places);

  } // namespace timer
} // namespace boost
```

--------------------------------

### Progress Display Class Synopsis (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/original_timer

Provides the C++ synopsis for the boost::progress_display class. It outlines the constructors, member functions like restart, operator+=, operator++, count, and expected_count, along with their effects and postconditions.

```cpp
#include <boost/progress.hpp>
namespace boost {
class progress_display : noncopyable {
 public:
   progress_display( unsigned long expected_count );
   // Effects: restart(expected_count)

   progress_display( unsigned long expected_count,
                     std::ostream& os,  // os is hint; implementation may ignore
                     const std::string & s1 = "\n", //leading strings
                     const std::string & s2 = "",
                     const std::string & s3 = "" )
   // Effects: save copy of leading strings, restart(expected_count)

   void           restart( unsigned long expected_count );
   //  Effects: display appropriate scale on three lines,
   //  prefaced by stored copy of s1, s2, s3, respectively, from constructor
   //  Postconditions: count()==0, expected_count()==expected_count

   unsigned long  operator+=( unsigned long increment )
   //  Effects: Display appropriate progress tic if needed.
   //  Postconditions: count()== original count() + increment
   //  Returns: count().

   unsigned long  operator++()
   //  Returns: operator+=( 1 ).

   unsigned long  count() const
   //  Returns: The internal count.

   unsigned long  expected_count() const
   //  Returns: The expected_count from the constructor.

   };
} // namespace boost
```

--------------------------------

### auto_cpu_timer Class Synopsis

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

This is the synopsis for the auto_cpu_timer class, which inherits from cpu_timer. It outlines the available constructors, destructor, observers, and actions. The constructors allow customization of output streams, precision (places), and format strings.

```cpp
class auto_cpu_timer : public cpu_timer
{
public:
  explicit auto_cpu_timer(short places = default_places);
           auto_cpu_timer(short places, const std::string& format);
  explicit auto_cpu_timer(const std::string& format);
           auto_cpu_timer(std::ostream& os, short places, const std::string& format);
  explicit auto_cpu_timer(std::ostream& os, short places = default_places);
           auto_cpu_timer(std::ostream& os, const std::string& format);

 ~auto_cpu_timer() noexcept;

  // compiler generated; shown for exposition only
  auto_cpu_timer(const auto_cpu_timer&) = default;
  auto_cpu_timer& operator=(const auto_cpu_timer&) = default;

  // observers
  std::ostream&      ostream() const noexcept;
  short              places() const noexcept;
  const std::string& format_string() const noexcept;

  // actions
  void               report();
};

```

--------------------------------

### auto_cpu_timer Constructors

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

These are the various constructors for the auto_cpu_timer class. They allow initialization with different combinations of precision (places), format strings, and output streams. If no ostream is specified, std::cout is used by default.

```cpp
explicit auto_cpu_timer(short places = default_places);
         auto_cpu_timer(short places, const std::string& format);
explicit auto_cpu_timer(const std::string& format);
         auto_cpu_timer(std::ostream& os, short places, const std::string& format);
explicit auto_cpu_timer(std::ostream& os, short places = default_places);
         auto_cpu_timer(std::ostream& os, const std::string& format);

```

--------------------------------

### Customizing auto_cpu_timer Output in C++

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Illustrates how to customize the output format and precision of `boost::timer::auto_cpu_timer` using constructor arguments. This allows control over the displayed information, such as units, number of decimal places, and the overall reporting string.

```cpp
boost::timer::auto_cpu_timer t;
// Default output: 5.713010s wall, 5.709637s user + 0.000000s system = 5.709637s CPU (99.9%)

boost::timer::auto_cpu_timer t(std::cerr, 2);
// Output with 2 decimal places: 5.71s wall, 5.70s user + 0.00s system = 5.70s CPU (99.9%)

boost::timer::auto_cpu_timer t(1);
// Output with 1 decimal place: 5.7s wall, 5.7s user + 0.0s system = 5.7s CPU (99.9%)

boost::timer::auto_cpu_timer t(3, "%w seconds\n");
// Custom format: 5.713 seconds

boost::timer::auto_cpu_timer t("%t sec CPU, %w sec real");
// Custom format: 5.709637 sec CPU, 5.713010 sec real
```

--------------------------------

### auto_cpu_timer format_string Observer

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

This observer function returns the format string used for reporting by the auto_cpu_timer. This format string is specified during construction or copy assignment.

```cpp
const std::string& format_string() const noexcept;

```

--------------------------------

### Format CPU Times to String (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Converts cpu_times values to strings representing seconds, formatted according to a specified format string. Supports default formatting and custom formats with placeholders for wall, user, system, total, and percentage times. Depends on the `cpu_times` struct.

```cpp
std::string format(const cpu_times& times, short places, const std::string& format);
std::string format(const cpu_times& times, short places = default_places);
```

--------------------------------

### Using cpu_timer for Checkpoints in C++

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Shows how to use `boost::timer::cpu_timer` to manually track elapsed time and create checkpoints. This approach is suitable for scenarios where timing needs to be sampled at specific intervals within a longer process, rather than just at the end of a scope.

```cpp
using boost::timer::cpu_timer;
using boost::timer::cpu_times;
using boost::timer::nanosecond_type;

...
nanosecond_type const twenty_seconds(20 * 1000000000LL);
nanosecond_type last(0);
cpu_timer timer;
while (more_transactions)
{
  process_a_transaction();
  cpu_times const elapsed_times(timer.elapsed());
  nanosecond_type const elapsed(elapsed_times.system
    + elapsed_times.user);
  if (elapsed >= twenty_seconds)
  {
    ... create a checkpoint ...
    last = elapsed;
  }
}
```

--------------------------------

### Boost Progress Timer Class Synopsis

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/original_timer

Defines the interface for the `boost::progress_timer` class, which inherits from `boost::timer` and automatically displays elapsed time upon destruction. It can be configured to use a specific output stream.

```cpp
#include <boost/progress.hpp>
namespace boost {
class progress_timer : public timer, noncopyable  {
 public:
   progress_timer();
   progress_timer( std::ostream& os ); // os is hint; implementation may ignore
   ~progress_timer();
   };
} // namespace boost

```

--------------------------------

### Basic Usage of progress_timer

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/original_timer

Demonstrates the simple usage of `boost::progress_timer` to measure the execution time of a block of code. An elapsed time message is automatically displayed when the `progress_timer` object goes out of scope.

```cpp
#include <boost/progress.hpp>
int main()
{
   progress_timer t;  // start timing
   // do something ...
   return 0;
}

```

--------------------------------

### auto_cpu_timer places Observer

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

This observer function returns the precision (number of decimal places) setting for the auto_cpu_timer. This value is set during construction or copy assignment.

```cpp
short places() const noexcept;

```

--------------------------------

### auto_cpu_timer ostream Observer

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

This observer function returns the output stream associated with the auto_cpu_timer object. This stream is determined during construction or via copy assignment.

```cpp
std::ostream& ostream() const noexcept;

```

--------------------------------

### auto_cpu_timer report Action

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

This action explicitly triggers the reporting of the elapsed CPU time. It formats the time using the specified precision and format string, and outputs it to the associated ostream. It's recommended to call stop() before report() for accurate results, and resume() can be called afterwards.

```cpp
void report();

```

--------------------------------

### CPU Timer Action: resume() (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Resumes accumulating elapsed time if the timer is in a stopped state. This method allows for continuous measurement across multiple start/stop intervals. If the timer is already running, this call has no effect.

```cpp
void resume() noexcept;
```

--------------------------------

### Boost Timer Class Synopsis

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/original_timer

Defines the interface for the `boost::timer` class, used for measuring elapsed time. It relies on the C Standard Library's `clock()` function, offering moderate portability but limited precision and a potentially short maximum measurable time.

```cpp
#include <boost/timer.hpp>
namespace boost {
class timer {
 public:
         timer();                        // postcondition: elapsed()==0
  // compiler generated copy constructor, copy assignment, and dtor apply
  void   restart();                      // post: elapsed()==0
  double elapsed() const;                // return elapsed time in seconds

  double elapsed_max() const;  // return estimated maximum value for elapsed()
  // Portability warning: elapsed_max() may return too high a value on systems
  // where std::clock_t overflows or resets at surprising values.

  double elapsed_min() const;            // return minimum value for elapsed()
  }; // timer
} // namespace boost

```

--------------------------------

### cpu_times Struct - Clear Function

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

The `clear()` function within the `cpu_times` struct resets all time components (wall, user, system) to zero. This is useful for re-initializing time measurements.

```c++
void clear();

// Effects: wall = user = system = 0LL.
```

--------------------------------

### auto_cpu_timer Destructor

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

The destructor for auto_cpu_timer. If the timer is running when the object goes out of scope, it will automatically stop the timer and report the elapsed CPU time. It is marked noexcept, ensuring no exceptions are thrown.

```cpp
~auto_cpu_timer() noexcept;

```

--------------------------------

### CPU Timer Action: stop() (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Stops the accumulation of elapsed time if the timer is currently running. This action records the elapsed time up to the point of the call, making it observable via `elapsed()`. After this call, the timer is in a stopped state (`is_stopped()`).

```cpp
void stop() noexcept;
```

--------------------------------

### CPU Timer Observer: is_stopped() (C++)

Source: https://www.boost.org/doc/libs/latest/libs/timer/doc/cpu_timers

Checks the current state of the `cpu_timer`. Returns `true` if the timer has been stopped by a call to `stop()`, indicating that further time accumulation has ceased. Otherwise, returns `false`.

```cpp
bool is_stopped() const noexcept;
```

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