目标

设计C++时间管理类，实现类似ROS中ros::Time::now()功能，能够直接输出double类型的时间戳。只不过有所变化：可以选择时间戳的精度。

实施

在函数体static TimeUtil now()中使用非静态变量时，会报错：

Error: invalid use of member in static member function

c++ - Error: invalid use of member in static member function - Stack Overflowhttps://stackoverflow.com/questions/17391853/error-invalid-use-of-member-in-static-member-functioninvalid use of member in static member function - arduino - Stack Overflowhttps://stackoverflow.com/questions/55105861/invalid-use-of-member-in-static-member-function-arduino

整体代码如下：

#ifndef TIME_UTIL_H_
#define TIME_UTIL_H_

#include <ctime>
#include <cstdlib>
#include <chrono>

enum TimeUnit{milliS, microS, nanoS}; //毫秒，微秒，纳秒, 默认微秒

class TimeUtil
{
 public:
    TimeUtil()
    {
    }

    TimeUtil(TimeUnit timeUnit)
    // :tu_(timeUnit)
    {
        tuS_ = timeUnit;
    }

    TimeUtil(const double &stamp)
        :now_(stamp * 1000)
    {
    }

    ~TimeUtil(){}

    static TimeUtil now()
    {
        TimeUtil t;
        switch (tuS_)
        {
        case milliS:
            t.now_ = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now().time_since_epoch()).count();
            break;
        case nanoS:
            t.now_ = std::chrono::duration_cast<std::chrono::nanoseconds>(std::chrono::system_clock::now().time_since_epoch()).count();
            break;
        default:
            t.now_ = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now().time_since_epoch()).count(); 
            break;
        }
        return t;
    }

    double toSec()
    {
        switch (tuS_)
        {
        case milliS:
            stamp_ = static_cast<double>(now_) * 0.001;
            break;
        case nanoS:
            stamp_ = static_cast<double>(now_) * 1.e-9;
            break;
        default:
            stamp_ = static_cast<double>(now_) * 1.e-6;
            break;
        }
        return stamp_;
    }

private:
    uint64_t now_;
    double stamp_;
    // TimeUnit tu_;
    static TimeUnit tuS_;
};

#endif