linux下時間的轉換 timeval /time_t time_t/tm

#include <stdio.h>
#include <stdlib.h>
//#include <sys/types.h>
#include <unistd.h>
#include <time.h>
#include <sys/time.h>

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

   struct    timeval t_startrun, t_endrun;
   int flag = 0;
  
   char   timef[100];
 time_t   t;
 struct   tm   *today;

    for( int i = 0 ; i < 1000 ; i++ )
  {
   gettimeofday(&t_startrun, 0 );
   usleep(1000000);
   gettimeofday(&t_endrun, 0);
   //printf("The program's running time is %ld ms! ",100);
   //printf("The program's running time is ms!");
      //(( t_endrun.tv_sec - t_startrun.tv_sec)*100000 + t_endrun.tv_usec - t_startrun.tv_usec) / 1000 );
      long ltime = (( t_endrun.tv_sec - t_startrun.tv_sec)*1000000 + t_endrun.tv_usec - t_startrun.tv_usec) / 1000 ;
      if( ltime < 0 )
      {
        printf("t_endrun.tv_sec = %d - t_startrun.tv_sec = %d,"
               "t_endrun.tv_usec = %d - t_startrun.tv_usec = %d/r/n",
               t_endrun.tv_sec , t_startrun.tv_sec,
               t_endrun.tv_usec , t_startrun.tv_usec);
      }
      t = t_endrun.tv_sec;
      today   =   localtime(&t);
     strftime(timef,100, "%Y-%m-%d   %H:%M:%S ",today);
     printf( "%d-%d,%d,%s/r/n ",t_endrun.tv_sec,t_endrun.tv_usec,t,timef);
      printf("The program's running time is %ld ms!/r/n ",ltime);
      fflush(stdout);
    }
  
    return 0;
}