Re: [boost] What else shall I do before reuse a stringstream for date parsing?

16 Feb 2009


      Bill David wrote:
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2009/2/16 Dmitry Goncharov <dgoncharov@unison.com>
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Bill David wrote:
...
To accelerate date parsing, I have writen a class to encapsulate the date
parsing logic as following.
But the second call to CDateParser::parseDate(str) always failed to parse
the date string. What else shall I do before reuse the stringstream
object?
#include <stdio.h>
#include <iostream>
#include <sstream>
using namespace std;
#include "boost/date_time/posix_time/posix_time.hpp"
using namespace boost::gregorian;
using namespace boost::posix_time;
class CDateParser
{
public:
   static void initialize();
   static time_t parseDate(const string& s);
private:
   static stringstream m_ss; //!< stringstream object used internally for
date parsing
};
stringstream CDateParser::m_ss;
time_t CDateParser::parseDate(const string& str)
{
   ptime p;
   m_ss.clear();
   m_ss << str;
   m_ss >> p;
   if (m_ss.fail()) {
       cout << "do not understand: " << str << endl;
       return 0;
   }
tm t = to_tm(p);
   return mktime(&t);
}
void CDateParser::initialize() {
   time_input_facet* timefacet = new time_input_facet("%a, %d %b %Y
%H:%M:%S %z"); // will be automatically deleted by related locale object
   m_ss.imbue(locale(locale::empty(), timefacet));
}
int main() {
   CDateParser::initialize();
string str;
   time_t t;
str = "Fri, 18 Jul 2008 11:53:14 GMT";
   t = CDateParser::parseDate(str);
   cout << ctime(&t) << endl;
str = "Sat, 19 Jul 2008 11:53:14 GMT";
   t = CDateParser::parseDate(str);
   cout << ctime(&t) << endl;
}
You should invoke m_ss.seekg(ios_base::beg) before each parsing.
Also, be careful with to_tm(). It is buggy. See
https://svn.boost.org/trac/boost/ticket/1859
But after I do that, both invocations report "do not understand".
And why clear can't rewind it?
It works for me. I also replaced locale:empty() (non-existent on my 
system) with locale() in order to compile your example.
BR, Dmitry
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