date and time temp update

Author: behnamfly

docs/date_time.md

@@ -1,4 +1,4 @@
-# Date and Time in C
+# 1. Date and Time in C
 1. `std::time()`: It returns the current time (seconds since 00:00:00 GMT, Jan 1, 1970) as an object of type `time_t`. `time_t` is defined as `int64` under the hood.
 
 2. `gmtime  (time_t *timer )`: converts given time since epoch into calendar time, expressed in Coordinated Universal Time (UTC) in the `struct tm` format. 
@@ -24,10 +24,79 @@ int main()
 }
 ```
 
-# Date and Time in C++
+# 2. Date and Time in C++
 
-`std::chrono::time_point`
+`template <class Clock, class Duration>  class time_point;`: This class expresses a point in time relative to a clock's epoch.
 
-`class system_clock`: It is the only C++ clock that has the ability to map its time points to C-style time
+## 2.1 Clock class:
+1. `system_clock`: is a system-wide realtime clock.
+2. `steady_clock`:  is specifically designed to calculate time intervals
+3. `high_resolution_clock`:  is the clock with the shortest tick period. It may be a synonym for `system_clock` or `steady_clock`.
+
+## 2.2 Duration class
+
+`template <class Rep, class Period = ratio<1> >class duration;`
+A duration object expresses a time span by means of a **count** (stored as an object of member type `rep`) and a **period**.
+
+
+
+
+```
+template<
+    class Rep,
+    class Period = std::ratio<1>
+> class duration;
+```
+Consists of the type of the tick `Rep` and the length of a tick `Period`.
+
+1. Rep: an arithmetic type representing the number of ticks
+2. Period: a `std::ratio` representing the tick period (number of second's fractions per tick)
+- `std::ratio<1,1>` stands for a second.
+- `std::ratio<1,60>` is a minute.
+- `std::ratio<1,1000>` is a millisecond.
+
+Predefined durations:
+
+```
+std::chrono::nanoseconds = typedef duration<signed int, std::nano> nanoseconds;
+std::chrono::microseconds = typedef duration<signed int, std::micro> microseconds;
+std::chrono::hours = typedef duration<signed int, ratio<3600>> hours;
+```
+
+
+
+## 2.3. std::chrono::time_point_cast
+
+Examples:
+
+`std::chrono::system_clock::now()` returns `std::chrono::time_point<std::chrono::system_clock, std::chrono::microseconds>`
+
+
+
+
+Different durations are not implicitly convertible to one another, You can have to convert time points with different durations using `std::chrono::time_point_cast`
+
+```cpp
+std::chrono::time_point<std::chrono::system_clock, std::chrono::nanoseconds> timePoint = 
+	std::chrono::time_point_cast<std::chrono::nanoseconds>(std::chrono::system_clock::now());
+```		  
+
+Refs: [1](https://stackoverflow.com/questions/15777073/how-do-you-print-a-c11-time-point), [2](https://www.modernescpp.com/index.php/time-duration), 
+[3](https://en.cppreference.com/w/cpp/chrono/duration)
+
+
+## 2.4.  std::chrono::duration_cast
+
+```cpp
+const auto now = std::chrono::system_clock::now();
+time_t time = std::chrono::system_clock::to_time_t(now);
+std::cout << time << "\n";
+std::cout << std::chrono::duration_cast<std::chrono::seconds>(now.time_since_epoch()).count() << "\n";
+std::cout << std::chrono::system_clock::from_time_t(time).time_since_epoch().count() << "\n";
+std::cout << std::chrono::system_clock::time_point(std::chrono::seconds(time)).time_since_epoch().count() << "\n";
+```
+
+Refs: [1](https://stackoverflow.com/questions/66346389/stdchronosystem-clock-and-c-time), [2](https://en.cppreference.com/w/cpp/chrono/duration/duration_cast)
+,[3](https://stackoverflow.com/questions/51538022/how-the-time-point-created-with-different-durationstdchronomilliseconds-and)
 
 [src](../src/date_time.cpp)

src/date_time.cpp

@@ -34,6 +34,7 @@ void cTime() {
   time_t epoch = std::time(NULL);
 
   std::cout << "seconds since the epoch began: " << epoch << std::endl;
+
   tm *t = gmtime(&epoch);
 
   std::cout << "current date and time: " << 1900 + t->tm_year << "/"
@@ -78,5 +79,40 @@ int main() {
 
   // std::cout << t_c << std::endl;
 
+  // std::chrono::nanoseconds is : typedef duration<signed int, std::nano>
+  // nanoseconds;
+
+  // timePoint = std::chrono::system_clock::now();
+
+  // std::chrono::system_clock::to_time_t(timePoint);
+
+  std::chrono::time_point<std::chrono::system_clock, std::chrono::nanoseconds>
+      timePoint = std::chrono::time_point_cast<std::chrono::nanoseconds>(
+          std::chrono::system_clock::now());
+
+  std::cout << timePoint << std::endl;
+  // std::cout << std::chrono::system_clock::to_time_t(timePoint) << std::endl;
+
+  std::cout << timePoint.time_since_epoch() << std::endl;
+
+  {
+    const auto now = std::chrono::system_clock::now();
+    time_t time = std::chrono::system_clock::to_time_t(now);
+    std::cout << time << "\n";
+    std::cout << std::chrono::duration_cast<std::chrono::seconds>(
+                     now.time_since_epoch())
+                     .count()
+              << "\n";
+    std::cout << std::chrono::system_clock::from_time_t(time)
+                     .time_since_epoch()
+                     .count()
+              << "\n";
+    std::cout << std::chrono::system_clock::time_point(
+                     std::chrono::seconds(time))
+                     .time_since_epoch()
+                     .count()
+              << "\n";
+  }
+
   return 0;
 }

src/regex_mathch_search.cpp

@@ -102,4 +102,92 @@ int main(int argc, char **argv) {
     std::cout << "match: " << match.suffix().str() << '\n';
     std::cout << "match: " << match.prefix().str() << '\n';
   }
-}
+
+  using namespace std::regex_constants;
+
+  std::cmatch m;
+
+  // std::regex_match("subject", m, std::regex("(sub)(.*)"));
+
+  std::regex_match(
+      "00000-2023-02-23_16-13-23.ulg_"
+      "06531353AC6AFC26C7633316B317B58A680E5D59039EE71E6D09B0A950A5F087.hash",
+      m, std::regex("00000-2023-02-23_16-13-23.ulg_[A-F0-9]*\\.hash"));
+
+  std::cout << "--------------"
+            << "\n";
+  std::string output = "matches:\n";
+  for (std::cmatch::iterator it = m.begin(); it != m.end(); ++it) {
+    std::cout << it->str() << "\n";
+    std::cout << "************"
+              << "\n";
+    output += it->str() + "\n";
+  }
+  std::cout << "......................"
+            << "\n";
+  std::cout << output << std::endl;
+
+  std::regex rx("00000-2023-02-23_16-13-23.ulg_[A-F0-9]*\\.hash");
+  std::cmatch mr;
+
+  std::regex_search(
+      "00000-2023-02-23_16-13-23.ulg_"
+      "06531353AC6AFC26C7633316B317B58A680E5D59039EE71E6D09B0A950A5F087.hash",
+      mr, rx);
+
+  std::csub_match sub = mr[1];
+  std::cout << "matched == " << std::boolalpha << sub.matched << std::endl;
+  std::cout << "length == " << sub.length() << std::endl;
+
+  std::csub_match::difference_type dif = std::distance(sub.first, sub.second);
+  std::cout << "difference == " << dif << std::endl;
+
+  std::csub_match::iterator first = sub.first;
+  std::csub_match::iterator last = sub.second;
+  std::cout << "range == " << std::string(first, last) << std::endl;
+  std::cout << "string == " << sub << std::endl;
+
+  std::csub_match::value_type const *ptr = "aab";
+  std::cout << "compare(\"aab\") == " << sub.compare(ptr) << std::endl;
+  std::cout << "compare(string) == " << sub.compare(std::string("AAA"))
+            << std::endl;
+  std::cout << "compare(sub) == " << sub.compare(sub) << std::endl;
+
+  std::string mainStr =
+      "00000-2023-02-23_16-13-23.ulg_"
+      "06531353AC6AFC26C7633316B317B58A680E5D59039EE71E6D09B0A950A5F087.hash";
+  std::string toErase = "00000-2023-02-23_16-13-23.ulg_";
+  size_t pos = mainStr.find(toErase);
+  if (pos != std::string::npos) {
+    // If found then erase it from string
+    mainStr.erase(pos, toErase.length());
+  }
+
+  toErase = ".hash";
+  pos = mainStr.find(toErase);
+
+  if (pos != std::string::npos) {
+    // If found then erase it from string
+    mainStr.erase(pos, toErase.length());
+  }
+
+  std::cout << mainStr;
+}
+
+// https://www.regular-expressions.info/dot.html
+// https://www3.ntu.edu.sg/home/ehchua/programming/howto/Regexe.html#:~:text=The%20%5C%20is%20known%20as%20the,have%20special%20meaning%20in%20regex.
+
+/*
+To match a string that contains only those characters (or an empty string), try
+"^[a-zA-Z0-9_]*$"
+
+^ : start of string
+[ : beginning of character group
+a-z : any lowercase letter
+A-Z : any uppercase letter
+0-9 : any digit
+_ : underscore
+] : end of character group
+* : zero or more of the given characters
+$ : end of string
+*/