Methods to Get System Time in Linux

The localtime function can be used to obtain the year, month, day, hour, minute, and second values separately.

　　C language implementation methods for obtaining system time in Linux:

　　1. The localtime function can be used to obtain the year, month, day, hour, minute, and second values separately.

　　```c 　　#include <time.h> //C language header file 　　#include <stdio.h> //C language I/O

　　void main () 　　{ 　　time_t now; // Instantiate time_t structure 　　struct tm *timenow; // Instantiate tm structure pointer 　　time(&now); 　　// The time function reads the current time (International Standard Time, not Beijing time) and passes the value to now 　　timenow = localtime(&now); 　　// The localtime function converts the time 'now' obtained from time() into the time on your computer (i.e., your configured region) 　　printf(" Local time is %s ",asctime(timenow)); 　　// In the above line, the asctime function converts the time to a string and outputs it via printf() 　　} 　　```

　　Note: time_t is a structure defined in time.h. The prototype of the tm structure is as follows:

　　c 　　struct tm 　　{ 　　int tm_sec;//seconds 0-61 　　int tm_min;//minutes 1-59 　　int tm_hour;//hours 0-23 　　int tm_mday;//day of the month 1-31 　　int tm_mon;//months since jan 0-11 　　int tm_year;//years from 1900 　　int tm_wday;//days since Sunday, 0-6 　　int tm_yday;//days since Jan 1, 0-365 　　int tm_isdst;//Daylight Saving time indicator 　　}; 　　

　　2. For certain requirements needing higher precision, Linux provides gettimeofday().

　　```c 　　#include <sys/time.h> 　　#include <stdio.h> 　　#include <unistd.h>

　　int main(int argc, char **argv) 　　{ 　　struct tim start,stop,diff; 　　gettimeofday(&start,0); 　　// Do what you need to do... 　　gettimeofday(&stop,0); 　　tim_subtract(&diff,&start,&stop); 　　printf("Total time taken: %d milliseconds ",diff.tv_usec); 　　}

　　int tim_subtract(struct tim *result, struct tim *x, struct tim *y) 　　{ 　　int nsec; 　　if ( x->tv_sec > y->tv_sec ) 　　return -1; 　　if ((x->tv_sec==y->tv_sec) && (x->tv_usec>y->tv_usec)) 　　return -1; 　　result->tv_sec = ( y->tv_sec-x->tv_sec ); result->tv_usec = ( y->tv_usec-x->tv_usec ); 　　if (result->tv_usec<0) 　　{ 　　result->tv_sec--; 　　result->tv_usec+=1000000; 　　} 　　return 0; 　　} 　　```