strftime.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <sys/time.h>
   4 #include <time.h>
   5
   6 static char *wday_ab[] = {
   7         "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
   8 };
   9 static char *wday[] = {
  10         "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
  11 };
  12 static char *mon_ab[] = {
  13         "Jan", "Feb", "Mar", "Apr", "May", "Jun",
  14         "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
  15 };
  16 static char *mon[] = {
  17         "January", "February", "March", "April", "May", "June",
  18         "July", "August", "September", "October", "November", "December"
  19 };
  20
  21 static char *putstr(char *d, char *s)
  22 {
  23         while (*s)
  24                 *d++ = *s++;
  25         return d;
  26 }
  27
  28 static char *puti(char *s, unsigned long n, int wid, int zpad)
  29 {
  30         int i;
  31         for (i = wid - 1; i >= 0; i--) {
  32                 if (!n) {
  33                         if (!zpad && i < wid - 1)
  34                                 s[i] = ' ';
  35                         else
  36                                 s[i] = '0';
  37                 } else {
  38                         s[i] = '0' + n % 10;
  39                         n /= 10;
  40                 }
  41         }
  42         return s + wid;
  43 }
  44
  45 static char *puttz(char *s)
  46 {
  47         int d = timezone / 60;
  48         if (d < 0) {
  49                 *s++ = '+';
  50                 d = -d;
  51         } else {
  52                 *s++ = '-';
  53         }
  54         s = puti(s, d / 60, 2, 1);
  55         s = puti(s, d % 60, 2, 1);
  56         return s;
  57 }
  58
  59 int strftime(char *s, int n, char *f, struct tm *tm)
  60 {
  61         int val;
  62         char *beg = s;
  63         char *e = s + n;
  64         while (s + 1 < e && *f) {
  65                 int c = *f++;
  66                 if (c != '%') {
  67                         *s++ = c;
  68                         continue;
  69                 }
  70                 c = *f++;
  71                 switch (c) {
  72                 case '%':
  73                         *s++ = '%';
  74                         break;
  75                 case 'a':
  76                         s = putstr(s, wday_ab[tm->tm_wday]);
  77                         break;
  78                 case 'A':
  79                         s = putstr(s, wday[tm->tm_wday]);
  80                         break;
  81                 case 'b':
  82                 case 'h':
  83                         s = putstr(s, mon_ab[tm->tm_mon]);
  84                         break;
  85                 case 'B':
  86                         s = putstr(s, mon[tm->tm_mon]);
  87                         break;
  88                 case 'c':
  89                         s += strftime(s, e - s, "%b %a %d %k:%M:%S %Z %Y", tm);
  90                         break;
  91                 case 'C':
  92                         s = puti(s, (1900 + tm->tm_year) / 100, 2, 1);
  93                         break;
  94                 case 'd':
  95                         s = puti(s, tm->tm_mday, 2, 1);
  96                         break;
  97                 case 'D':
  98                         s += strftime(s, e - s, "%m/%d/%y", tm);
  99                         break;
 100                 case 'e':
 101                         s = puti(s, tm->tm_mday, 2, 0);
 102                         break;
 103                 case 'F':
 104                         s += strftime(s, e - s, "%Y/%m/%d", tm);
 105                         break;
 106                 case 'H':
 107                         s = puti(s, tm->tm_hour, 2, 1);
 108                         break;
 109                 case 'I':
 110                         val = tm->tm_hour > 12 ? tm->tm_hour - 12 : tm->tm_hour;
 111                         s = puti(s, val ? val : 12, 2, 1);
 112                         break;
 113                 case 'j':
 114                         s = puti(s, tm->tm_yday + 1, 3, 1);
 115                         break;
 116                 case 'k':
 117                         s = puti(s, tm->tm_hour, 2, 1);
 118                         break;
 119                 case 'm':
 120                         s = puti(s, tm->tm_mon + 1, 2, 1);
 121                         break;
 122                 case 'M':
 123                         s = puti(s, tm->tm_min, 2, 1);
 124                         break;
 125                 case 'n':
 126                         *s++ = '\n';
 127                         break;
 128                 case 'p':
 129                         s = putstr(s, tm->tm_hour >= 12 ? "PM" : "AM");
 130                         break;
 131                 case 'P':
 132                         s = putstr(s, tm->tm_hour >= 12 ? "pm" : "am");
 133                         break;
 134                 case 'r':
 135                         s += strftime(s, e - s, "%I:%M:%S %p", tm);
 136                         break;
 137                 case 'R':
 138                         s += strftime(s, e - s, "%H:%M", tm);
 139                         break;
 140                 case 'S':
 141                         s = puti(s, tm->tm_sec, 2, 1);
 142                         break;
 143                 case 't':
 144                         *s++ = '\t';
 145                         break;
 146                 case 'T':
 147                         s += strftime(s, e - s, "%H:%M:%S", tm);
 148                         break;
 149                 case 'u':
 150                         s = puti(s, tm->tm_wday ? tm->tm_wday : 7, 1, 0);
 151                         break;
 152                 case 'w':
 153                         s = puti(s, tm->tm_wday, 1, 0);
 154                         break;
 155                 case 'x':
 156                         s += strftime(s, e - s, "%b %a %d", tm);
 157                         break;
 158                 case 'X':
 159                         s += strftime(s, e - s, "%k:%M:%S", tm);
 160                         break;
 161                 case 'y':
 162                         s = puti(s, tm->tm_year % 100, 2, 1);
 163                         break;
 164                 case 'Y':
 165                         s = puti(s, 1900 + tm->tm_year, 4, 1);
 166                         break;
 167                 case 'z':
 168                         s = puttz(s);
 169                         break;
 170                 default:
 171                         break;
 172                 }
 173         }
 174         *s = '\0';
 175         return s - beg;
 176 }