簡單介紹
strptime()函式可以依照特定時間格式將字串轉換為時間型別。簡單點說可以將字串時間轉化為時間戳。
這個函式包括在time.h標頭檔案裡，在Unix或者類Unix系統中，我們會常常接觸到。可是到了跑Nuttx系統的Pixhawk。真是醉了，非常多東西都沒有，或者少了非常多東西，比方time.h中就沒有這個函式的實現，又如dirent.h中的一些檔案型別的巨集定義也沒有了。
可是我們非常須要，比方在時間的比較上，我們不能去拿字串去操作來比較。會搞死人的。直接得到時間戳，三下兩除二就搞定了。那就要用到strptime這個函式了。
實現
mystrptime.c
/*
* Note:因time.h中沒有strptime函式(UNIX中是有的)，本檔案是對strptime功能的自己定義實現；
* We do not implement alternate representations. However, we always
* check whether a given modifier is allowed for a certain conversion.
*/
#include "mystrptime.h"
static const char *day[7] = {
"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday",
"Friday", "Saturday"
};
static const char *abday[7] = {
"Sun","Mon","Tue","Wed","Thu","Fri","Sat"
};
static const char *mon[12] = {
"January", "February", "March", "April", "May", "June", "July",
"August", "September", "October", "November", "December"
};
static const char *abmon[12] = {
"Jan", "Feb", "Mar", "Apr", "May", "Jun",
"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};
static const char *am_pm[2] = {
"AM", "PM"
};
static int conv_num(const char **buf, int *dest, int llim, int ulim)
{
int result = 0;
/* The limit also determines the number of valid digits. */
int rulim = ulim;
if (**buf < '0' || **buf > '9')
return (0);
do {
result *= 10;
result += *(*buf)++ - '0';
rulim /= 10;
} while ((result * 10 <= ulim) && rulim && **buf >= '0' && **buf <= '9');
if (result < llim || result > ulim)
return (0);
*dest = result;
return (1);
}
char * mystrptime(const char *buf, const char *fmt, struct tm *tm)
{
char c;
const char *bp;
size_t len = 0;
int alt_format, i, split_year = 0;
bp = buf;
while ((c = *fmt) != '\0') {
/* Clear `alternate' modifier prior to new conversion. */
alt_format = 0;
/* Eat up white-space. */
if (isspace(c)) {
while (isspace(*bp))
bp++;
fmt++;
continue;
}
if ((c = *fmt++) != '%')
goto literal;
again: switch (c = *fmt++) {
case '%': /* "%%" is converted to "%". */
literal:
if (c != *bp++)
return (0);
break;
/*
* "Alternative" modifiers. Just set the appropriate flag
* and start over again.
*/
case 'E': /* "%E?" alternative conversion modifier. */
LEGAL_ALT(0);
alt_format |= ALT_E;
goto again;
case 'O': /* "%O?" alternative conversion modifier. */
LEGAL_ALT(0);
alt_format |= ALT_O;
goto again;
/*
* "Complex" conversion rules, implemented through recursion.
*/
case 'c': /* Date and time, using the locale's format. */
LEGAL_ALT(ALT_E);
if (!(bp = mystrptime(bp, "%x %X", tm)))
return (0);
break;
case 'D': /* The date as "%m/%d/%y". */
LEGAL_ALT(0);
if (!(bp = mystrptime(bp, "%m/%d/%y", tm)))
return (0);
break;
case 'R': /* The time as "%H:%M". */
LEGAL_ALT(0);
if (!(bp = mystrptime(bp, "%H:%M", tm)))
return (0);
break;
case 'r': /* The time in 12-hour clock representation. */
LEGAL_ALT(0);
if (!(bp = mystrptime(bp, "%I:%M:%S %p", tm)))
return (0);
break;
case 'T': /* The time as "%H:%M:%S". */
LEGAL_ALT(0);
if (!(bp = mystrptime(bp, "%H:%M:%S", tm)))
return (0);
break;
case 'X': /* The time, using the locale's format. */
LEGAL_ALT(ALT_E);
if (!(bp = mystrptime(bp, "%H:%M:%S", tm)))
return (0);
break;
case 'x': /* The date, using the locale's format. */
LEGAL_ALT(ALT_E);
if (!(bp = mystrptime(bp, "%m/%d/%y", tm)))
return (0);
break;
/*
* "Elementary" conversion rules.
*/
case 'A': /* The day of week, using the locale's form. */
case 'a':
LEGAL_ALT(0);
for (i = 0; i < 7; i++) {
/* Full name. */
len = strlen(day[i]);
if (strncasecmp(day[i], bp, len) == 0)
break;
/* Abbreviated name. */
len = strlen(abday[i]);
if (strncasecmp(abday[i], bp, len) == 0)
break;
}
/* Nothing matched. */
if (i == 7)
return (0);
tm->tm_wday = i;
bp += len;
break;
case 'B': /* The month, using the locale's form. */
case 'b':
case 'h':
LEGAL_ALT(0);
for (i = 0; i < 12; i++) {
/* Full name. */
len = strlen(mon[i]);
if (strncasecmp(mon[i], bp, len) == 0)
break;
/* Abbreviated name. */
len = strlen(abmon[i]);
if (strncasecmp(abmon[i], bp, len) == 0)
break;
}
/* Nothing matched. */
if (i == 12)
return (0);
tm->tm_mon = i;
bp += len;
break;
case 'C': /* The century number. */
LEGAL_ALT(ALT_E);
if (!(conv_num(&bp, &i, 0, 99)))
return (0);
if (split_year) {
tm->tm_year = (tm->tm_year % 100) + (i * 100);
} else {
tm->tm_year = i * 100;
split_year = 1;
}
break;
case 'd': /* The day of month. */
case 'e':
LEGAL_ALT(ALT_O);
if (!(conv_num(&bp, &tm->tm_mday, 1, 31)))
return (0);
break;
case 'k': /* The hour (24-hour clock representation). */
LEGAL_ALT(0);
/* FALLTHROUGH */
case 'H':
LEGAL_ALT(ALT_O);
if (!(conv_num(&bp, &tm->tm_hour, 0, 23)))
return (0);
break;
case 'l': /* The hour (12-hour clock representation). */
LEGAL_ALT(0);
/* FALLTHROUGH */
case 'I':
LEGAL_ALT(ALT_O);
if (!(conv_num(&bp, &tm->tm_hour, 1, 12)))
return (0);
if (tm->tm_hour == 12)
tm->tm_hour = 0;
break;
case 'j': /* The day of year. */
LEGAL_ALT(0);
if (!(conv_num(&bp, &i, 1, 366)))
return (0);
tm->tm_yday = i - 1;
break;
case 'M': /* The minute. */
LEGAL_ALT(ALT_O);
if (!(conv_num(&bp, &tm->tm_min, 0, 59)))
return (0);
break;
case 'm': /* The month. */
LEGAL_ALT(ALT_O);
if (!(conv_num(&bp, &i, 1, 12)))
return (0);
tm->tm_mon = i - 1;
break;
case 'p': /* The locale's equivalent of AM/PM. */
LEGAL_ALT(0);
/* AM? */
if (strcasecmp(am_pm[0], bp) == 0) {
if (tm->tm_hour > 11)
return (0);
bp += strlen(am_pm[0]);
break;
}
/* PM? */
else if (strcasecmp(am_pm[1], bp) == 0) {
if (tm->tm_hour > 11)
return (0);
tm->tm_hour += 12;
bp += strlen(am_pm[1]);
break;
}
/* Nothing matched. */
return (0);
case 'S': /* The seconds. */
LEGAL_ALT(ALT_O);
if (!(conv_num(&bp, &tm->tm_sec, 0, 61)))
return (0);
break;
case 'U': /* The week of year, beginning on sunday. */
case 'W': /* The week of year, beginning on monday. */
LEGAL_ALT(ALT_O);
/*
* XXX This is bogus, as we can not assume any valid
* information present in the tm structure at this
* point to calculate a real value, so just check the
* range for now.
*/
if (!(conv_num(&bp, &i, 0, 53)))
return (0);
break;
case 'w': /* The day of week, beginning on sunday. */
LEGAL_ALT(ALT_O);
if (!(conv_num(&bp, &tm->tm_wday, 0, 6)))
return (0);
break;
case 'Y': /* The year. */
LEGAL_ALT(ALT_E);
if (!(conv_num(&bp, &i, 0, 9999)))
return (0);
tm->tm_year = i - TM_YEAR_BASE;
break;
case 'y': /* The year within 100 years of the epoch. */
LEGAL_ALT(ALT_E | ALT_O);
if (!(conv_num(&bp, &i, 0, 99)))
return (0);
if (split_year) {
tm->tm_year = ((tm->tm_year / 100) * 100) + i;
break;
}
split_year = 1;
if (i <= 68)
tm->tm_year = i + 2000 - TM_YEAR_BASE;
else
tm->tm_year = i + 1900 - TM_YEAR_BASE;
break;
/*
* Miscellaneous conversions.
*/
case 'n': /* Any kind of white-space. */
case 't':
LEGAL_ALT(0);
while (isspace(*bp))
bp++;
break;
default: /* Unknown/unsupported conversion. */
return (0);
}
}
/* LINTED functional specification */
return ((char *)bp);
}
time_t to_seconds(const char *date,int mode)
{
struct tm storage={0,0,0,0,0,0,0,0,0};
char *p=NULL;
time_t retval=0;
if(1 == mode)p=(char *)mystrptime(date,"%Y-%m-%d",&storage);
else if(0 == mode)p=(char *)mystrptime(date,"%Y_%m_%d",&storage);
if(p==NULL)
{
retval=0;
}
else
{
retval=mktime(&storage);
}
return retval;
}
mystrptime.h
#ifndef MYSTRPTIME_H_
#define MYSTRPTIME_H_
#include <stdio.h>
#include <time.h>
#include <ctype.h>
#include <string.h>
#define ALT_E 0x01
#define ALT_O 0x02
#define LEGAL_ALT(x) { if (alt_format & ~(x)) return (0); }
#define TM_YEAR_BASE 1900
char *mystrptime(const char *buf, const char *fmt, struct tm *tm);
time_t to_seconds(const char *date,int mode);
#endif測試
/*Test*/
/*
#intclude <stdio.h>
#include "mystrptime.h"
int main ()
{
time_t ts;
ts = to_seconds("2015-07-29",1);
//ts = to_seconds("2015_07_29",0);
printf("ts=%d\n",ts);
return(0);
}
*/