C/C++获取时间戳和计算时间差

#include 
#include 
#include 
#include          // std::this_thread::sleep_for
#include 

int main001()
{
    std::time_t t = std::time(0);  // t is an integer type
    std::cout << t << " seconds since 01-Jan-1970\n";
    return 0;
}


int main002()
{
    unsigned long int sec1 = time(NULL);
    time_t sec2 = time(NULL);  // 这里的time_t不是std:time_t
    std::cout << sec1 << std::endl;
    std::cout << sec2 << std::endl;
    return 0;
}

// C/C++获取时间戳和计算时间差
int main003()
{

    std::chrono::milliseconds ms = std::chrono::duration_cast< std::chrono::milliseconds >(std::chrono::system_clock::now().time_since_epoch());
	long start= ms.count();
	
    std::cout << ms.count() << std::endl;
	std::cout << "start="<(std::chrono::system_clock::now().time_since_epoch());
	long end= ms.count();
	std::cout << "end="<(std::chrono::system_clock::now().time_since_epoch());
	long start= ms.count();
	
    std::cout << ms.count() << std::endl;
	
	std::cout << "start="<(std::chrono::system_clock::now().time_since_epoch());
	long end= ms.count();
	std::cout << "end="<