分享C++11代码片段－tuple和chrono

缺乏、安全感 2022-07-16 02:23 146阅读 0赞

元组，我也不清楚，c++是不是借鉴了python从而引入了元组。

tuple元组定义了一个有固定数目元素的容器,其中的每个元素类型都可以不相同,这与其他容器有着本质的区别.是对pair的泛化。

首先来介绍元组的创建和元组元素的访问。通过make\_tuple()创建元组，通过get<>()来访问元组的元素。

**tuple**

#include <iostream>
    #include <tuple>
    
    using namespace std;
    
    int main() {
      tuple<int, string, double> firstRecord(42, "myFirstName", 1.303);
      tuple<int, string, double> secondRecord(21, "mySecondName", 2.638);
    
      auto concat = tuple_cat(firstRecord, secondRecord);
    
      /* for printing a tuple of any size you have to recursively use templates */
      cout << get<1>(concat) << " " << get<4>(concat) << endl;
    
    
      const int a = 1;
      const int b = 2;
      const double x = 2.34;
      const double y = 4.27;
    
      /* tie creates a tuple from lvalue references */
      if(tie(a, x) < tie(b, y))
        cout << "second arguments are larger" << endl;
    
      /* * use this to easily implement e.g. * bool operator<(const A& rhs) const { return tie(n, s, d) < tie(rhs.n, rhs.s, rhs.d); } */
    
    
      int f = 1;
      int g = 2;
      int h = 3;
    
      /* unpack variables */
      tie(f, g, h) = tie(g, f, h);
    
      cout << "f " << f << ", g " << g << ", h " << h << endl;
      /* * f=2, g=2, h=3, because it is evaluated as follows: * f = g; -> f=2 * g = f; -> g=2 * h = h; -> h=3 */
    }

**chrono**  
chrono是一个time library, 源于boost，现在已经是C++标准。

要使用chrono库，需要\#include，其所有实现均在std::chrono namespace下。注意标准库里面的每个命名空间代表了一个独立的概念。所以下文中的概念均以命名空间的名字表示！ chrono是一个模版库，使用简单，功能强大，只需要理解三个概念：duration、time\_point、clock

#include <iostream>
    #include <chrono>
    #include <thread>
    
    using namespace std;
    
    int main() {
      /* * nanoseconds * microseconds * milliseconds * seconds * minutes * hours */
    
      const chrono::seconds sec(chrono::hours(1) + chrono::minutes(9) + chrono::seconds(8));
      cout << "1h 9m 8s = " << sec.count() << "s" << endl;
    
      /* get the duration of a section */
      const auto start(chrono::steady_clock::now());
      this_thread::sleep_for(chrono::seconds(3));
      const auto end(chrono::steady_clock::now());
    
      chrono::nanoseconds duration(end - start);
    
      cout << "duration of section: " << duration.count() << "ns"<< endl;
      cout << "duration of section: " << chrono::duration_cast<chrono::microseconds>(duration).count() << "ms"<< endl;
    }