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

From: Andrew Holden (aholden_at_[hidden])
Date: 2006-03-21 17:17:53

> -----Original Message-----
> From: Christian Henning [mailto:chhenning_at_[hidden]]
> Sent: Tuesday, March 21, 2006 4:23 PM
> To: boost-users_at_[hidden]
> 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