How to compare dates, entered as strings, C/C++
I need a way to compare dates when entered by a user as as string, as in "July 15, 200" vs "May 16, 1999".
I was thinking something along the line of creating an enum say for the months;
typedef enu {
january = 0,
february = 1,
and so on...
}eMonth;
then maybe an array:
string sYear[] = {"january ", "february ", and so on};
Then looping through sYear to get a match for the month then setting a local eMonth variable to corresponding enum in the typedef enum for eMonth. But this seems like a lot of work I'd think there must be an easier way.
And NO the user can not enter the string as mm/dd/yyyy, it has to be in the form I stated above.
Thanks
I was thinking something along the line of creating an enum say for the months;
typedef enu {
january = 0,
february = 1,
and so on...
}eMonth;
then maybe an array:
string sYear[] = {"january ", "february ", and so on};
Then looping through sYear to get a match for the month then setting a local eMonth variable to corresponding enum in the typedef enum for eMonth. But this seems like a lot of work I'd think there must be an easier way.
And NO the user can not enter the string as mm/dd/yyyy, it has to be in the form I stated above.
Thanks
I'm sure you can find a library out there that has done this. Need help looking for one? (if so, what environment are you developing in?)
ASKER
I really don't want a library(dll or something) I want to add the code myself for future maintenance and portability.
To you want to WRITE it too? There are open source libraries out there too.
If you DO want to write it, then I think you are indeed headed down the right track: you are definitely going to want an array of strings that contain the month names for comparison to your input string. I recommend you make these stored array strings all caps, (or all lowercase), then convert the input to match (before your compare loop).
Do you need to consider "Jan", "Jan." and those variations too?
If you DO want to write it, then I think you are indeed headed down the right track: you are definitely going to want an array of strings that contain the month names for comparison to your input string. I recommend you make these stored array strings all caps, (or all lowercase), then convert the input to match (before your compare loop).
Do you need to consider "Jan", "Jan." and those variations too?
An 'enum' type certainly is not the most efficiant solution to look up vaues from strings - a map might be more approptiate, e.g.
#include <string
#include <map>
using namespace std;
// ...
map<string, int> mapMonths;
mapMonths.insert(map<string, int>::value_type("January",1);
mapMonths.insert(map<string, int>::value_type("February",2);
// ...
mapMonths.insert(map<string, int>::value_type("December",12);
// there's also room for e.g. mapMonths.insert(map<string, int>::value_type("Jan",1);
// ...
// Look up the value
map<string, int>::iterator i = mapMonths.find("March");
if (i != mapMonths.end()) { // found something!
int nMonthNum = i->second;
}ASKER
Korbus,
Open source would work, you have any suggestions?
Thanks
Open source would work, you have any suggestions?
Thanks
I would be doing little more than searching http://sourceforge.net/ (an excellent resource) for you, as I have not used such a library myself. Perhaps another expert will have a suggestion on a (tested) library.
In Unix, there is strptime that might help you. But from your previous questions, I believe you are working on Windows. No such thing there. Below is open source code that you can try to get to work on Windows. But first, here is an example of its usage.
http://pubs.opengroup.org/onlinepubs/7999959899/functions/strptime.html
Open source version taken from:
http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/time/strptime.c?rev=HEAD
http://pubs.opengroup.org/onlinepubs/7999959899/functions/strptime.html
#include <time.h>
...
struct tm tm;
time_t t;
if (strptime("6 Dec 2001 12:33:45", "%d %b %Y %H:%M:%S", &tm) == NULL)
/* Handle error */;
printf("year: %d; month: %d; day: %d;\n",
tm.tm_year, tm.tm_mon, tm.tm_mday);
printf("hour: %d; minute: %d; second: %d\n",
tm.tm_hour, tm.tm_min, tm.tm_sec);
printf("week day: %d; year day: %d\n", tm.tm_wday, tm.tm_yday);
tm.tm_isdst = -1; /* Not set by strptime(); tells mktime()
to determine whether daylight saving time
is in effect */
t = mktime(&tm);
if (t == -1)
/* Handle error */;
printf("seconds since the Epoch: %ld\n", (long) t);"Open source version taken from:
http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/time/strptime.c?rev=HEAD
/* $NetBSD: strptime.c,v 1.38 2013/05/17 12:55:57 joerg Exp $ */
/*-
* Copyright (c) 1997, 1998, 2005, 2008 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code was contributed to The NetBSD Foundation by Klaus Klein.
* Heavily optimised by David Laight
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: strptime.c,v 1.38 2013/05/17 12:55:57 joerg Exp $");
#endif
#include "namespace.h"
#include <sys/localedef.h>
#include <ctype.h>
#include <locale.h>
#include <string.h>
#include <time.h>
#include <tzfile.h>
#include "private.h"
#include "setlocale_local.h"
#ifdef __weak_alias
__weak_alias(strptime,_strptime)
__weak_alias(strptime_l, _strptime_l)
#endif
#define _TIME_LOCALE(loc) \
((_TimeLocale *)((loc)->part_impl[(size_t)LC_TIME]))
/*
* We do not implement alternate representations. However, we always
* check whether a given modifier is allowed for a certain conversion.
*/
#define ALT_E 0x01
#define ALT_O 0x02
#define LEGAL_ALT(x) { if (alt_format & ~(x)) return NULL; }
static char gmt[] = { "GMT" };
static char utc[] = { "UTC" };
/* RFC-822/RFC-2822 */
static const char * const nast[5] = {
"EST", "CST", "MST", "PST", "\0\0\0"
};
static const char * const nadt[5] = {
"EDT", "CDT", "MDT", "PDT", "\0\0\0"
};
static const u_char *conv_num(const unsigned char *, int *, uint, uint);
static const u_char *find_string(const u_char *, int *, const char * const *,
const char * const *, int);
char *
strptime(const char *buf, const char *fmt, struct tm *tm)
{
return strptime_l(buf, fmt, tm, _current_locale());
}
char *
strptime_l(const char *buf, const char *fmt, struct tm *tm, locale_t loc)
{
unsigned char c;
const unsigned char *bp, *ep;
int alt_format, i, split_year = 0, neg = 0, offs;
const char *new_fmt;
bp = (const u_char *)buf;
while (bp != NULL && (c = *fmt++) != '\0') {
/* Clear `alternate' modifier prior to new conversion. */
alt_format = 0;
i = 0;
/* Eat up white-space. */
if (isspace(c)) {
while (isspace(*bp))
bp++;
continue;
}
if (c != '%')
goto literal;
again: switch (c = *fmt++) {
case '%': /* "%%" is converted to "%". */
literal:
if (c != *bp++)
return NULL;
LEGAL_ALT(0);
continue;
/*
* "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. */
new_fmt = _TIME_LOCALE(loc)->d_t_fmt;
goto recurse;
case 'D': /* The date as "%m/%d/%y". */
new_fmt = "%m/%d/%y";
LEGAL_ALT(0);
goto recurse;
case 'F': /* The date as "%Y-%m-%d". */
new_fmt = "%Y-%m-%d";
LEGAL_ALT(0);
goto recurse;
case 'R': /* The time as "%H:%M". */
new_fmt = "%H:%M";
LEGAL_ALT(0);
goto recurse;
case 'r': /* The time in 12-hour clock representation. */
new_fmt = _TIME_LOCALE(loc)->t_fmt_ampm;
LEGAL_ALT(0);
goto recurse;
case 'T': /* The time as "%H:%M:%S". */
new_fmt = "%H:%M:%S";
LEGAL_ALT(0);
goto recurse;
case 'X': /* The time, using the locale's format. */
new_fmt = _TIME_LOCALE(loc)->t_fmt;
goto recurse;
case 'x': /* The date, using the locale's format. */
new_fmt = _TIME_LOCALE(loc)->d_fmt;
recurse:
bp = (const u_char *)strptime((const char *)bp,
new_fmt, tm);
LEGAL_ALT(ALT_E);
continue;
/*
* "Elementary" conversion rules.
*/
case 'A': /* The day of week, using the locale's form. */
case 'a':
bp = find_string(bp, &tm->tm_wday,
_TIME_LOCALE(loc)->day, _TIME_LOCALE(loc)->abday, 7);
LEGAL_ALT(0);
continue;
case 'B': /* The month, using the locale's form. */
case 'b':
case 'h':
bp = find_string(bp, &tm->tm_mon,
_TIME_LOCALE(loc)->mon, _TIME_LOCALE(loc)->abmon,
12);
LEGAL_ALT(0);
continue;
case 'C': /* The century number. */
i = 20;
bp = conv_num(bp, &i, 0, 99);
i = i * 100 - TM_YEAR_BASE;
if (split_year)
i += tm->tm_year % 100;
split_year = 1;
tm->tm_year = i;
LEGAL_ALT(ALT_E);
continue;
case 'd': /* The day of month. */
case 'e':
bp = conv_num(bp, &tm->tm_mday, 1, 31);
LEGAL_ALT(ALT_O);
continue;
case 'k': /* The hour (24-hour clock representation). */
LEGAL_ALT(0);
/* FALLTHROUGH */
case 'H':
bp = conv_num(bp, &tm->tm_hour, 0, 23);
LEGAL_ALT(ALT_O);
continue;
case 'l': /* The hour (12-hour clock representation). */
LEGAL_ALT(0);
/* FALLTHROUGH */
case 'I':
bp = conv_num(bp, &tm->tm_hour, 1, 12);
if (tm->tm_hour == 12)
tm->tm_hour = 0;
LEGAL_ALT(ALT_O);
continue;
case 'j': /* The day of year. */
i = 1;
bp = conv_num(bp, &i, 1, 366);
tm->tm_yday = i - 1;
LEGAL_ALT(0);
continue;
case 'M': /* The minute. */
bp = conv_num(bp, &tm->tm_min, 0, 59);
LEGAL_ALT(ALT_O);
continue;
case 'm': /* The month. */
i = 1;
bp = conv_num(bp, &i, 1, 12);
tm->tm_mon = i - 1;
LEGAL_ALT(ALT_O);
continue;
case 'p': /* The locale's equivalent of AM/PM. */
bp = find_string(bp, &i, _TIME_LOCALE(loc)->am_pm,
NULL, 2);
if (tm->tm_hour > 11)
return NULL;
tm->tm_hour += i * 12;
LEGAL_ALT(0);
continue;
case 'S': /* The seconds. */
bp = conv_num(bp, &tm->tm_sec, 0, 61);
LEGAL_ALT(ALT_O);
continue;
#ifndef TIME_MAX
#define TIME_MAX INT64_MAX
#endif
case 's': /* seconds since the epoch */
{
time_t sse = 0;
uint64_t rulim = TIME_MAX;
if (*bp < '0' || *bp > '9') {
bp = NULL;
continue;
}
do {
sse *= 10;
sse += *bp++ - '0';
rulim /= 10;
} while ((sse * 10 <= TIME_MAX) &&
rulim && *bp >= '0' && *bp <= '9');
if (sse < 0 || (uint64_t)sse > TIME_MAX) {
bp = NULL;
continue;
}
if (localtime_r(&sse, tm) == NULL)
bp = NULL;
}
continue;
case 'U': /* The week of year, beginning on sunday. */
case 'W': /* The week of year, beginning on monday. */
/*
* 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.
*/
bp = conv_num(bp, &i, 0, 53);
LEGAL_ALT(ALT_O);
continue;
case 'w': /* The day of week, beginning on sunday. */
bp = conv_num(bp, &tm->tm_wday, 0, 6);
LEGAL_ALT(ALT_O);
continue;
case 'u': /* The day of week, monday = 1. */
bp = conv_num(bp, &i, 1, 7);
tm->tm_wday = i % 7;
LEGAL_ALT(ALT_O);
continue;
case 'g': /* The year corresponding to the ISO week
* number but without the century.
*/
bp = conv_num(bp, &i, 0, 99);
continue;
case 'G': /* The year corresponding to the ISO week
* number with century.
*/
do
bp++;
while (isdigit(*bp));
continue;
case 'V': /* The ISO 8601:1988 week number as decimal */
bp = conv_num(bp, &i, 0, 53);
continue;
case 'Y': /* The year. */
i = TM_YEAR_BASE; /* just for data sanity... */
bp = conv_num(bp, &i, 0, 9999);
tm->tm_year = i - TM_YEAR_BASE;
LEGAL_ALT(ALT_E);
continue;
case 'y': /* The year within 100 years of the epoch. */
/* LEGAL_ALT(ALT_E | ALT_O); */
bp = conv_num(bp, &i, 0, 99);
if (split_year)
/* preserve century */
i += (tm->tm_year / 100) * 100;
else {
split_year = 1;
if (i <= 68)
i = i + 2000 - TM_YEAR_BASE;
else
i = i + 1900 - TM_YEAR_BASE;
}
tm->tm_year = i;
continue;
case 'Z':
tzset();
if (strncmp((const char *)bp, gmt, 3) == 0) {
tm->tm_isdst = 0;
#ifdef TM_GMTOFF
tm->TM_GMTOFF = 0;
#endif
#ifdef TM_ZONE
tm->TM_ZONE = gmt;
#endif
bp += 3;
} else {
ep = find_string(bp, &i,
(const char * const *)tzname,
NULL, 2);
if (ep != NULL) {
tm->tm_isdst = i;
#ifdef TM_GMTOFF
tm->TM_GMTOFF = -(timezone);
#endif
#ifdef TM_ZONE
tm->TM_ZONE = tzname[i];
#endif
}
bp = ep;
}
continue;
case 'z':
/*
* We recognize all ISO 8601 formats:
* Z = Zulu time/UTC
* [+-]hhmm
* [+-]hh:mm
* [+-]hh
* We recognize all RFC-822/RFC-2822 formats:
* UT|GMT
* North American : UTC offsets
* E[DS]T = Eastern : -4 | -5
* C[DS]T = Central : -5 | -6
* M[DS]T = Mountain: -6 | -7
* P[DS]T = Pacific : -7 | -8
* Military
* [A-IL-M] = -1 ... -9 (J not used)
* [N-Y] = +1 ... +12
*/
while (isspace(*bp))
bp++;
switch (*bp++) {
case 'G':
if (*bp++ != 'M')
return NULL;
/*FALLTHROUGH*/
case 'U':
if (*bp++ != 'T')
return NULL;
/*FALLTHROUGH*/
case 'Z':
tm->tm_isdst = 0;
#ifdef TM_GMTOFF
tm->TM_GMTOFF = 0;
#endif
#ifdef TM_ZONE
tm->TM_ZONE = utc;
#endif
continue;
case '+':
neg = 0;
break;
case '-':
neg = 1;
break;
default:
--bp;
ep = find_string(bp, &i, nast, NULL, 4);
if (ep != NULL) {
#ifdef TM_GMTOFF
tm->TM_GMTOFF = -5 - i;
#endif
#ifdef TM_ZONE
tm->TM_ZONE = __UNCONST(nast[i]);
#endif
bp = ep;
continue;
}
ep = find_string(bp, &i, nadt, NULL, 4);
if (ep != NULL) {
tm->tm_isdst = 1;
#ifdef TM_GMTOFF
tm->TM_GMTOFF = -4 - i;
#endif
#ifdef TM_ZONE
tm->TM_ZONE = __UNCONST(nadt[i]);
#endif
bp = ep;
continue;
}
if ((*bp >= 'A' && *bp <= 'I') ||
(*bp >= 'L' && *bp <= 'Y')) {
#ifdef TM_GMTOFF
/* Argh! No 'J'! */
if (*bp >= 'A' && *bp <= 'I')
tm->TM_GMTOFF =
('A' - 1) - (int)*bp;
else if (*bp >= 'L' && *bp <= 'M')
tm->TM_GMTOFF = 'A' - (int)*bp;
else if (*bp >= 'N' && *bp <= 'Y')
tm->TM_GMTOFF = (int)*bp - 'M';
#endif
#ifdef TM_ZONE
tm->TM_ZONE = NULL; /* XXX */
#endif
bp++;
continue;
}
return NULL;
}
offs = 0;
for (i = 0; i < 4; ) {
if (isdigit(*bp)) {
offs = offs * 10 + (*bp++ - '0');
i++;
continue;
}
if (i == 2 && *bp == ':') {
bp++;
continue;
}
break;
}
switch (i) {
case 2:
offs *= 100;
break;
case 4:
i = offs % 100;
if (i >= 60)
return NULL;
/* Convert minutes into decimal */
offs = (offs / 100) * 100 + (i * 50) / 30;
break;
default:
return NULL;
}
if (neg)
offs = -offs;
tm->tm_isdst = 0; /* XXX */
#ifdef TM_GMTOFF
tm->TM_GMTOFF = offs;
#endif
#ifdef TM_ZONE
tm->TM_ZONE = NULL; /* XXX */
#endif
continue;
/*
* Miscellaneous conversions.
*/
case 'n': /* Any kind of white-space. */
case 't':
while (isspace(*bp))
bp++;
LEGAL_ALT(0);
continue;
default: /* Unknown/unsupported conversion. */
return NULL;
}
}
return __UNCONST(bp);
}
static const u_char *
conv_num(const unsigned char *buf, int *dest, uint llim, uint ulim)
{
uint result = 0;
unsigned char ch;
/* The limit also determines the number of valid digits. */
uint rulim = ulim;
ch = *buf;
if (ch < '0' || ch > '9')
return NULL;
do {
result *= 10;
result += ch - '0';
rulim /= 10;
ch = *++buf;
} while ((result * 10 <= ulim) && rulim && ch >= '0' && ch <= '9');
if (result < llim || result > ulim)
return NULL;
*dest = result;
return buf;
}
static const u_char *
find_string(const u_char *bp, int *tgt, const char * const *n1,
const char * const *n2, int c)
{
int i;
size_t len;
/* check full name - then abbreviated ones */
for (; n1 != NULL; n1 = n2, n2 = NULL) {
for (i = 0; i < c; i++, n1++) {
len = strlen(*n1);
if (strncasecmp(*n1, (const char *)bp, len) == 0) {
*tgt = i;
return bp + len;
}
}
}
/* Nothing matched */
return NULL;
}
You probably should become familiar with ctime:
http://www.cplusplus.com/reference/ctime/
as well as the other functions at the bottom under "See also".
http://www.cplusplus.com/reference/ctime/
as well as the other functions at the bottom under "See also".
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