C 日期和時(shí)間函數(shù)

#include <stdio.h> 
#include <time.h> 
#include <math.h> 
#include <ctype.h> 

int main(void) { 
  time_t calendar_start = time(NULL);         // Initial calendar time 
  clock_t cpu_start = clock();                // Initial processor time 
  int count = 0;                              // Count of number of loops 
  const long long iterations = 1000000000LL;  // Loop iterations 
  char answer = "y"; 
  double x = 0.0; 
  printf("Initial clock time = %lld Initial calendar time = %lld\n", 
            (long long)cpu_start, (long long)calendar_start); 
  while(tolower(answer) == "y") { 
    for(long long i = 0LL ; i < iterations ; ++i) 
      x = sqrt(3.14159265); 
  
    printf("%lld square roots completed.\n", iterations*(++count)); 
    printf("Do you want to run some more(y or n)? \n"); 
    scanf("\n%c", &answer, sizeof(answer)); 
  } 
  
  clock_t cpu_end = clock();                  // Final cpu time 
  time_t calendar_end = time(NULL);           // Final calendar time 
  
  printf("Final clock time = %lld Final calendar time = %lld\n", 
     (long long)cpu_end, (long long)calendar_end); 
  printf("CPU time for %lld iterations is %.2lf seconds\n", 
     count*iterations, ((double)(cpu_end-cpu_start))/CLOCKS_PER_SEC); 
  printf("Elapsed calendar time to execute the program is %8.2lf seconds.\n", 
     difftime(calendar_end, calendar_start)); 
  return 0; 
} 

#include <stdio.h> 
#include <time.h> 

int main(void) 
{ 
  const char *day[7] = { 
                   "Sunday"  , "Monday", "Tuesday", "Wednesday", 
                   "Thursday", "Friday", "Saturday" 
                       }; 
  const char *month[12] = { 
                     "January",   "February", "March",    "April", 
                     "May",       "June",     "July",     "August", 
                     "September", "October",  "November", "December" 
                          }; 
  const char *suffix[] = { "st", "nd", "rd", "th" }; 
  enum sufindex { st, nd, rd, th } sufsel = th;       // Suffix selector 
  
  struct tm ourT;                                     // The time structure 
  time_t tVal = time(NULL);                           // Calendar time 
  
  if(!localtime_s(&tVal, &ourT))                      // Populate time structure 
  { 
    fprintf(stderr, "Failed to populate tm struct.\n"); 
    return -1; 
  } 
  switch(ourT.tm_mday) 
  { 
    case 1: case 21: case 31: 
      sufsel= st; 
      break; 
    case 2: case 22: 
      sufsel= nd; 
      break; 
    case 3: case 23: 
      sufsel= rd; 
      break; 
    default: 
      sufsel= th; 
      break; 
  } 
  
  printf("Today is %s the %d%s %s %d. ", 
      day[ourT.tm_wday], 
      ourT.tm_mday, 
      suffix[sufsel], 
      month[ourT.tm_mon], 
      1900 + ourT.tm_year); 
  printf("The time is %d : %d : %d.\n", 
      ourT.tm_hour, ourT.tm_min, ourT.tm_sec ); 
  return 0; 
}

#include <stdio.h> 
#include <time.h> 

int main(void) 
{ 
  const char *day[7] = { 
                   "Sunday"  , "Monday", "Tuesday", "Wednesday", 
                   "Thursday", "Friday", "Saturday" 
                       }; 
  const char *month[12] = { 
                     "January",   "February", "March",    "April", 
                     "May",       "June",     "July",     "August", 
                     "September", "October",  "November", "December" 
                          }; 
  const char *suffix[] = { "st", "nd", "rd", "th" }; 
  enum sufindex { st, nd, rd, th } sufsel = th;  // Suffix selector 
  
  struct tm birthday = {0};                      // A birthday time structure 
  char name[30] = {"C"}; 
  
  printf("Enter the birthday as day month year integers separated by spaces." 
             "\ne.g. Enter 1st February 1985 as 1 2 1985 : "); 
  scanf(" %d %d %d", &birthday.tm_mday, &birthday.tm_mon, &birthday.tm_year); 
  
  birthday.tm_mon -= 1;                          // Month zero-based 
  birthday.tm_year -= 1900;                      // Year relative to 1900 
  
  if(mktime(&birthday) == - 1) 
  { 
    fprintf_s(stderr, "Operation failed.\n"); 
    return -1; 
  } 
  
  switch(birthday.tm_mday) 
  { 
    case 1: case 21: case 31: 
      sufsel= st; 
      break; 
    case 2: case 22: 
      sufsel= nd; 
      break; 
    case 3: case 23: 
      sufsel= rd; 
      break; 
    default: 
      sufsel= th; 
      break; 
  } 
  printf("born on the %d%s %s %d, which was a %s.\n", 
                 birthday.tm_mday, suffix[sufsel], month[birthday.tm_mon], 
                            1900 + birthday.tm_year, day[birthday.tm_wday]); 
  return 0; 
}