C++：獲取時間戳

文中代碼主要來自

• http://stackoverflow.com/questions/6012663/get-unix-timestamp-with-c
• http://stackoverflow.com/questions/19555121/how-to-get-current-timestamp-in-milliseconds-since-1970-just-the-way-java-gets
• http://stackoverflow.com/questions/2831841/how-to-get-time-in-millis-in-c-just-like-java

1.獲取以秒爲單位的時間戳

1.1 C++風格

#include <iostream>
#include <ctime>

int main()
{
    std::time_t t = std::time(0);  // t is an integer type
    std::cout << t << " seconds since 01-Jan-1970\n";
    return 0;
}

編譯運行：

$ g++ -Wall test.cpp 
$ ./a.out 
1467214075 seconds since 01-Jan-1970

1.2 C風格

#include <iostream>
#include <sys/time.h>

int main()
{
    unsigned long int sec1 = time(NULL);
    time_t sec2 = time(NULL);  // 這裏的time_t不是std:time_t
    std::cout << sec1 << std::endl;
    std::cout << sec2 << std::endl;
    return 0;
}

編譯運行：

$ g++ -Wall test.cpp 
$ ./a.out 
1467214468
1467214468

2.獲取以毫秒爲單位的時間戳

2.1 C++風格

#include <iostream>
#include <chrono>

int main()
{

    std::chrono::milliseconds ms = std::chrono::duration_cast< std::chrono::milliseconds >(
        std::chrono::system_clock::now().time_since_epoch()
    );

    std::cout << ms.count() << std::endl;
    return 0;
}

編譯運行：

$ g++ -std=c++11 -Wall test.cpp 
$ ./a.out 
1467215317714

std::chrono屬於C++ 11.

相關：

• http://en.cppreference.com/w/cpp/chrono/duration
• http://www.cplusplus.com/reference/chrono/duration/

2.2 C風格

#include <iostream>
#include <sys/time.h>

int main()
{
    struct timeval tp;
    gettimeofday(&tp, NULL);
    long int ms = tp.tv_sec * 1000 + tp.tv_usec / 1000;
    std:: cout << ms << std::endl;
    return 0;
}

編譯運行：

$ g++  -Wall test.cpp 
$ ./a.out 
1467215481946