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

Subject: Re: [boost] What else shall I do before reuse a stringstream for date parsing?
From: Dmitry Goncharov (dgoncharov_at_[hidden])
Date: 2009-02-16 04:53:43

Bill David wrote:
> 2009/2/16 Dmitry Goncharov <dgoncharov_at_[hidden]>
>
>   
>> 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
>
>