仿ROS的C++版本时间管理类

1. 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。不过有所变化：可以选择时间戳的精度；

2. 可以获取时间段，比如用于计算频率/帧率，统计代码耗时等。

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 
#include 
#include 

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::system_clock::now().time_since_epoch()).count();
            break;
        case nanoS:
            t.now_ = std::chrono::duration_cast(std::chrono::system_clock::now().time_since_epoch()).count();
            break;
        default:
            t.now_ = std::chrono::duration_cast(std::chrono::system_clock::now().time_since_epoch()).count(); 
            break;
        }
        return t;
    }

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

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

#endif

 因为ROS的多了一个精度选择，所以需要变量，完全仿ROS的话，使用时要给static TimeUnit tuS_;在目标对象定义一次，不大好用。

c++ - Undefined reference to static variable - Stack Overflowhttps://stackoverflow.com/questions/14331469/undefined-reference-to-static-variable

因此就不完全仿ROS的格式，改成以下代码算了：

#ifndef TIME_UTIL_H_
#define TIME_UTIL_H_

#include 
#include 
#include 

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

class TimeUtil
{
 public:
    TimeUtil()
    {
    }

    TimeUtil(TimeUnit timeUnit)
    :tu_(timeUnit)
    {
    }

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

    ~TimeUtil(){}

    TimeUtil now()
    {
        TimeUtil t;
        switch (tu_)
        {
        case milliS:
            t.now_ = std::chrono::duration_cast(std::chrono::system_clock::now().time_since_epoch()).count();
            break;
        case nanoS:
            t.now_ = std::chrono::duration_cast(std::chrono::system_clock::now().time_since_epoch()).count();
            break;
        default:
            t.now_ = std::chrono::duration_cast(std::chrono::system_clock::now().time_since_epoch()).count(); 
            break;
        }
        return t;
    }

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

private:
    uint64_t now_;
    double stamp_;
    TimeUnit tu_;
};

使用时定义一下，就可以获得double类型的时间戳了。

    TimeUtil stamp;
    cout << "fusion and vo calibration first time: " << stamp.now().toSec() << endl;

整体代码如下：

class TicToc
{
public:
    TicToc()
    {
        tic();
    }

    void tic()
    {
        start = std::chrono::system_clock::now();
    }

    double toc()
    {
        end = std::chrono::system_clock::now();
        std::chrono::duration elapsed_seconds = end - start;
        return elapsed_seconds.count() * 1000;
    }

private:
    std::chrono::time_point start, end;
};