Re: [Boost-users] [date_time] How to create a date from string withspecific format?

21 Mar 2006

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-----Original Message-----
From: Christian Henning [mailto:chhenning@gmail.com]
Sent: Tuesday, March 21, 2006 4:23 PM
To: boost-users@lists.boost.org
Subject: Re: [Boost-users] [date_time] How to create a date from
string
withspecific format?
Hi Dean, thanks for the answer.
Since, I know the format of the date strings I could also use
boost::regex for the general format and then feeding a date object
with the values. If I get an exception during the date object
contruction I know that the user provided me with garbage.

...
Any thoughts on that?
Thanks again,
Christian
Have you considered using Regex's submatches?  A slightly modified
example follows.

   // date format: mm-dd-yyyy
   boost::regex oDateReg( "(\\d{2})-(\\d{2})-(\\d{4})" );
   std::string strDate( "11-33-1997" );
   boost::smatch dateMatch;

   if( boost::regex_match( strDate
                         , dateMatch
                         , oDateReg ))
   {
      try
      {
         std::string strMonth = dateMatch[1];
         std::string strDay   = dateMatch[2];
         std::string strYear  = dateMatch[3];

         unsigned int nYear  = boost::lexical_cast<unsigned
int>(strYear);
         unsigned int nMonth = boost::lexical_cast<unsigned
int>(strMonth);
         unsigned int nDay   = boost::lexical_cast<unsigned
int>(strDay);

         date d( nYear, nMonth, nDay );

         date::ymd_type ymd = d.year_month_day();
      }
      catch( std::out_of_range oEx )
      {
         std::cout << "Error: " << oEx.what() << std::endl;
      }
   }

There are two advantages to this.  First, you no longer need to count
characters when extracting the date components.  Second, you have a
little more freedom in defining your date format.  For example, you
could use the following definition for oDateReg to also accept
single-digit months and/or days:
   boost::regex oDateReg( "(\\d{1,2})-(\\d{1,2})-(\\d{4})" );

Andrew Holden