错误：'high_resolution_clock‘尚未声明

Question

我在Windows10上使用的是g++ 8.1.0版，但在尝试编译时仍在使用

auto start=high_resolution_clock::now();
rd(n);
auto stop=high_resolution_clock::now();
auto duration = duration_cast<microseconds>(stop-start);
cout<<duration.count()<<endl;

我得到的错误是

error: 'high_resolution_clock' has not been declared
 auto start=high_resolution_clock::now();
            ^~~~~~~~~~~~~~~~~~~~~

我已经包含了chrono和time.h。

Answer 1

您需要在high_resolution_clock、microseconds和duration_cast前面指定std::chrono::名称空间限定符，例如：

#include <chrono>

auto start = std::chrono::high_resolution_clock::now();
rd(n);
auto stop = std::chrono::high_resolution_clock::now();
auto duration = std::chrono::duration_cast<std::chrono::microseconds>(stop-start);
std::cout << duration.count() << std::endl;

否则，您可以改用using语句，例如：

#include <chrono>
using namespace std::chrono;

auto start = high_resolution_clock::now();
rd(n);
auto stop = high_resolution_clock::now();
auto duration = duration_cast<microseconds>(stop-start);
std::cout << duration.count() << std::endl;

或者：

#include <chrono>
using std::chrono::high_resolution_clock;
using std::chrono::microseconds;
using std::chrono::duration_cast;

auto start = high_resolution_clock::now();
rd(n);
auto stop = high_resolution_clock::now();
auto duration = duration_cast<microseconds>(stop-start);
std::cout << duration.count() << std::endl;

Answer 2

哦，我刚得到解决方案，我忘了使用时序命名空间，所以代码应该是：

auto start=chrono::high_resolution_clock::now();
rd(n);
auto stop=chrono::high_resolution_clock::now();
auto duration = chrono::duration_cast<chrono::microseconds>(stop-start);
cout<<duration.count()<<endl;