[Boost-users] boost::posix_time::ptime - Parsing time - clarification

[Rakesh Kumar]

Hi,
I was going through the API to parse a date-time
field. I came across the boost library regarding the
same.


#include "boost/date_time/posix_time/posix_time.hpp"

using namespace boost::posix_time;
#include <iostream>
#include <cstdlib>

using std::cout;

int main() {
std::string ts("2002-01-20 23:59:59.000");
ptime t(time_from_string(ts));

cout << to_simple_string(t);
return EXIT_SUCCESS;
}

This example compiled fine and gave me the right
results. But suppose if I have another date
representation as follows.

06 Dec 2004 10:40:58.000

If I enter the same string and try to parse from it,
the method time_from_string aborts. I was wondering if
there is any way I can tell time_from_string the
format and try to parse from it.



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[Jeff Garland]

On Sun, 19 Dec 2004 22:22:46 -0800 (PST), Rakesh Kumar wrote

> Hi,
> I was going through the API to parse a date-time
> field. I came across the boost library regarding the
> same.
>
> #include "boost/date_time/posix_time/posix_time.hpp"
>
> using namespace boost::posix_time;
> #include <iostream>
> #include <cstdlib>
>
> using std::cout;
>
> int main() {
> std::string ts("2002-01-20 23:59:59.000");
> ptime t(time_from_string(ts));
>
> cout << to_simple_string(t);
> return EXIT_SUCCESS;
> }
>
> This example compiled fine and gave me the right
> results. But suppose if I have another date
> representation as follows.
>
> 06 Dec 2004 10:40:58.000
>
> If I enter the same string and try to parse from it,
> the method time_from_string aborts. I was wondering if
> there is any way I can tell time_from_string the
> format and try to parse from it.

Well, there isn't currently a way to tell from_string to do this directly.
However, you can use functions from the library to write your own parsing
routine. For example, the following handles the format you provided:

boost::posix_time::ptime
my_parse_time(const std::string& s)
{
using namespace boost::gregorian;
using namespace boost::posix_time;
std::string date_part(s.substr(0,11));
date d = from_uk_string(date_part); //expects day month year order
std::string time_part(s.substr(12,12));
time_duration td = duration_from_string(time_part);
return ptime(d, td);
}

int
main()
{
using namespace boost::posix_time;
using namespace boost::gregorian;
std::string ts("06 Dec 2004 23:59:59.000");
try {
ptime t = my_parse_time(ts);
std::cout << to_simple_string(t) << std::endl;
}
catch(std::exception& e) {} // invalid time string
return 0;

}

In the 1.33 release you will be able to pass a format to a facet class to
adjust how you want things parsed. It will look like this:

std::stringstream ss("06 Dec 2004 23:59:59.000");
time_facet* tf = new time_facet("%d %M %Y %H:%M:%s");
ss.imbue(tf);
ptime t; //not-a-date-time
ss >> t;

Jeff

[Rakesh Kumar]

Thanks Jeff for the detailed example.

Eagerly looking forward to the 1.33 release.

--- Jeff Garland <je...@crystalclearsoftware.com>
wrote:

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