Re: Converting date string to a number

From:
=?ISO-8859-1?Q?Erik_Wikstr=F6m?= <Erik-wikstrom@telia.com>
Newsgroups:
comp.lang.c++
Date:
Wed, 18 Jul 2007 11:30:00 GMT
Message-ID:
<YQmni.4318$ZA.2030@newsb.telia.net>
On 2007-07-18 13:21, Jef Driesen wrote:

Jim Langston wrote:

"Jef Driesen" <jefdriesen@hotmail.com.invalid> wrote in message
news:f7kkqb$487$1@ikaria.belnet.be...

How can I convert a date string to a number (e.g. a time_t value or a tm
struct)? I know about the strptime function, but then I have to know the
format string. And that is a problem.

I'm trying to autoformat the contents of text entries in a GUI. For
numbers, I'm converting the text representation to the appropriate type
(using atoi, atof, ...) and converting the result back to text with the
correct format (using sprintf). But this does not work for date (or time)
strings.

For instance, if the desired date format is "dd-mm-yy", but the user
enters "dd-mm-yyyy", I can't convert the string to a valid date, because I
don't know its format.


atoi, atof, etc.. are a pain in the neck. If you use stringstream it's
rather easy.

std::cout << "Enter Date:";
std::cin >> Date;
std::stringstream Stream(Date);
int Month, Day, Year;
char Hyphen;

if ( Stream >> Month >> Hyphen >> Day >> Hyphen >> Year )
   // Got good date. Values in Month, Day and year. Should validate them
somehow
else
   // Something went wrong, not in right format.

The good thing about this is, you don't have to care how long the month, day
or year entries are. They could enter a 1 or 100 digit number, and it would
read it. Of course, after this is done you want to do reality checking.
I.E. Is month 1-12? Is day 1-31? If year is 2 digit, do you want to add
1900 or 2000? If year is 4 digit, is it realistic? Etc...


This approach using stringstream has (almost) the same problem. You
still need to know the order of the 'components'. And that can be
different in another locale:

yyyy-mm-dd (ISO)
dd/mm/yyyy (Europe)
mm/dd/yyyy (US)

I don't need to be able to handle all possible formats, because that is
impossible (e.g. is 01/01/2007 a European or a US style date?). But I do
want to handle some minor variations of the preferred format, like the 2
or 4 digit year, a change in hyphen (- or /) and things like that.


If you fix the order (ie. must be year, month, day) you should be able
to let the user separate them however he likes, and also use as many
number of digits for each field as he wishes.

--
Erik Wikstr?m

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