Get the uptime of the system

There are several ways:

1. Execute command uptime

2. Using the Clock_gettime function and the SysInfo function

#include <time.h>
#include <sys/times.h>
#include <unistd.h>
#include <sys/  sysinfo.h>

void Main (void)
{
struct TIMESPEC tp;  
clock_gettime (Clock_monotonic, &TP);  
//clock_t ticks = times (NULL);  
//printf ("Seconds:%d\n", ticks/sysconf (_SC_CLK_TCK));  
printf ("Up Time:%f\n", Tp.tv_sec + (float) tp.tv_nsec/1000000000);    

struct SysInfo info;
SysInfo (&info);

printf ("Up Time (sysinfo.uptime):%d\n", info.uptime);
} 

3 views/proc/uptime

Here's a look at the results:

$./a.out;uptime;cat/proc/uptime up
time:4581.407706
-Time (sysinfo.uptime): 4582
 02:05:45 up  1:16 ,  3 users,  load average:0.08, 0.45, 0.95
4581.41 14391.24

The following code uses SysInfo to calculate when the system starts:

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

int main (void)
{
	struct sysinfo info;
	SysInfo (&info);

	time_t boottime = Time (NULL)-info.uptime;

	struct Timespec monotime;
	Clock_gettime (Clock_monotonic, &monotime);
	
	time_t curtime = Boottime + monotime.tv_sec;

	struct Timespec realtime;
	Clock_gettime (Clock_realtime, &realtime);

	printf ("Boot time =%s", CTime (&boottime));
	printf ("Current time =%s", CTime (&curtime));
	printf ("Real time =%s", CTime (&realtime.tv_sec));

	return 0;
}

Execution Result:

$./a.out 
Boot time = Thu  1 00:49:23 Current time
= Thu  1 02:08:17
Real time = Thu M AY  1 02:08:18 2014