C++ 获取时间间隔

clock函数方式

Linux平台下C/C++中获取时间间隔的方法，一种比较普遍的认识是采用clock函数

clock_t clock ( void );

Returns the number of clock ticks elapsed since the program was launched.

The macro constant expression CLOCKS_PER_SEC specifies the relation between a clock tick and a second (clock ticks per second).

The initial moment of reference used by clock as the beginning of the program execution may vary between platforms. To calculate the actual processing times of a program, the value returned by clock should be compared to a value returned by an initial call to clock.

通过两次调用clock函数可以得到起始时间和结束时间，从而得到毫秒级的时间差

gettimeofday函数方式

C/C++语言中有个timeval结构是可以精确到毫秒，可以利用timeval来记录起始时间和结束时间

           struct timeval {
               time_t      tv_sec;     /* seconds */
               SUSEconds_t tv_usec;    /* microseconds */
           };

通过调用gettimeofday函数可以得到用timeval结构记录的当前时间

int gettimeofday(struct timeval *tv, struct timezone *tz);

具体实现

#include <time.h>

#include <sys/time.h>

class ClockTool
{
    public:
    ClockTool()
        : m_begin(0), m_end(0)
    {
    }

    inline void begin()
    {
        m_begin = clock();
    }

    inline void end()
    {
        m_end = clock();
    }

    inline void reset()
    {
        m_begin = 0;
        m_end = 0;
    }

    float getInterval()
    {
        if (m_end < m_begin)
        {
            return 0;
        }
        return (double)(m_end - m_begin)/CLOCKS_PER_SEC;
    }

    private:
    clock_t m_begin;
    clock_t m_end;
};

class TimeTool
{
    public:
    TimeTool()
    {
        reset();
    }

    inline void begin()
    {
        gettimeofday(&m_begin, NULL);
    }

    inline void end()
    {
        gettimeofday(&m_end, NULL);
    }

    inline void reset()
    {
        memset(&m_begin, 0, sizeof(struct timeval));
        memset(&m_end, 0, sizeof(struct timeval));
    }

    float getInterval()
    {
        if (m_end.tv_usec < m_begin.tv_usec)
        {
            m_end.tv_usec += 1000;
            m_end.tv_sec = m_end.tv_sec - 1;
        }
        return (m_end.tv_sec - m_begin.tv_sec) + (m_end.tv_usec - m_begin.tv_usec) / 1000000.0;
    }

    private:
    struct timeval m_begin;
    struct timeval m_end;
};

测试clock函数与gettimeofday函数的执行效率

#include <stdio.h>


#include <string.h>
#include "clocktool.h"


int main(int argc, char** argv)
{

const int iLoop = 100000000;


TimeTool tool;
tool.begin();
struct timeval stick0;
for (int i = 0; i < iLoop; ++i)
{
memset(&stick0, 0, sizeof(struct timeval));
gettimeofday(&stick0, NULL);
}
tool.end();
printf("cost %f\n", tool.getInterval());


tool.reset();


tool.begin();


clock_t stick1= 0;
for (int i = 0; i < iLoop; ++i)
{
stick1 = clock();
}
tool.end();


printf("cost %f\n", tool.getInterval());
}



执行测试可以发现gettimeofday函数的执行效率远高于clock函数

注：发现该测试结论和环境有些相关，有些环境下两者差别没有这么大(并且编译时是否带优化选项-O2对clock的执行效率也影响比较大)，比较接近，但总体而言gettimeofday仍优于clock

cost 2.469688
cost 26.162617