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#include <time.h>
#include <string.h>
static char *awday[7] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
static char *wday[7] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday",
"Friday", "Saturday"};
static char *amon[12] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun",
"Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };
static char *mon[12] = {"January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November", "December"};
static char *ampm[2] = {"AM", "PM"};
static char *tz[2] = {"EST", "EDT"};
static int jan1(int);
static char *strval(char *, char *, char **, int, int);
static char *dval(char *, char *, int, int);
size_t
strftime(char *s, size_t maxsize, const char *format, const struct tm *t)
{
char *sp, *se, *fp;
int i;
sp = s;
se = s+maxsize;
for(fp=(char *)format; *fp && sp<se; fp++){
if(*fp != '%')
*sp++ = *fp;
else switch(*++fp){
case 'a':
sp = strval(sp, se, awday, t->tm_wday, 7);
break;
case 'A':
sp = strval(sp, se, wday, t->tm_wday, 7);
break;
case 'b':
sp = strval(sp, se, amon, t->tm_mon, 12);
break;
case 'B':
sp = strval(sp, se, mon, t->tm_mon, 12);
break;
case 'c':
sp += strftime(sp, se-sp, "%a %b %d %H:%M:%S %Y", t);
break;
case 'd':
sp = dval(sp, se, t->tm_mday, 2);
break;
case 'H':
sp = dval(sp, se, t->tm_hour, 2);
break;
case 'I':
i = t->tm_hour;
if(i == 0)
i = 12;
else if(i > 12)
i -= 12;
sp = dval(sp, se, i, 2);
break;
case 'j':
sp = dval(sp, se, t->tm_yday+1, 3);
break;
case 'm':
sp = dval(sp, se, t->tm_mon+1, 2);
break;
case 'M':
sp = dval(sp, se, t->tm_min, 2);
break;
case 'p':
i = (t->tm_hour < 12)? 0 : 1;
sp = strval(sp, se, ampm, i, 2);
break;
case 'S':
sp = dval(sp, se, t->tm_sec, 2);
break;
case 'U':
i = 7-jan1(t->tm_year);
if(i == 7)
i = 0;
/* Now i is yday number of first sunday in year */
if(t->tm_yday < i)
i = 0;
else
i = (t->tm_yday-i)/7 + 1;
sp = dval(sp, se, i, 2);
break;
case 'w':
sp = dval(sp, se, t->tm_wday, 1);
break;
case 'W':
i = 8-jan1(t->tm_year);
if(i >= 7)
i -= 7;
/* Now i is yday number of first monday in year */
if(t->tm_yday < i)
i = 0;
else
i = (t->tm_yday-i)/7 + 1;
sp = dval(sp, se, i, 2);
break;
case 'x':
sp += strftime(sp, se-sp, "%a %b %d, %Y", t);
break;
case 'X':
sp += strftime(sp, se-sp, "%H:%M:%S", t);
break;
case 'y':
sp = dval(sp, se, t->tm_year%100, 2);
break;
case 'Y':
sp = dval(sp, se, t->tm_year+1900, 4);
break;
case 'Z':
/* hack for now: assume eastern time zone */
i = t->tm_isdst? 1 : 0;
sp = strval(sp, se, tz, i, 2);
break;
case 0:
fp--; /* stop loop after next fp incr */
break;
default:
*sp++ = *fp;
}
}
if(*fp)
sp = s; /* format string didn't end: no room for conversion */
if(sp<se)
*sp = 0;
return sp-s;
}
static char *
strval(char *start, char *end, char **array, int index, int alen)
{
int n;
if(index<0 || index>=alen){
*start = '?';
return start+1;
}
n = strlen(array[index]);
if(n > end-start)
n = end-start;
memcpy(start, array[index], n);
return start+n;
}
static char *
dval(char *start, char *end, int val, int width)
{
char *p;
if(val<0 || end-start<width){
*start = '?';
return start+1;
}
p = start+width-1;
while(p>=start){
*p-- = val%10 + '0';
val /= 10;
}
if(val>0)
*start = '*';
return start+width;
}
/*
* return day of the week
* of jan 1 of given year
*/
static int
jan1(int yr)
{
int y, d;
/*
* normal gregorian calendar
* one extra day per four years
*/
y = yr+1900;
d = 4+y+(y+3)/4;
/*
* julian calendar
* regular gregorian
* less three days per 400
*/
if(y > 1800) {
d -= (y-1701)/100;
d += (y-1601)/400;
}
/*
* great calendar changeover instant
*/
if(y > 1752)
d += 3;
return(d%7);
}
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