boost_1_45_0/libs/date_time/xmldoc/io_tutorial.xml

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     Subject to the Boost Software License, Version 1.0. 
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<section id="date_time.io_tutorial" 
  xmlns:xi="http://www.w3.org/2001/XInclude">
  <title>Date Time IO Tutorial</title>
  <bridgehead renderas="sect2">Date Time IO Tutorial</bridgehead>

  <link linkend="basic_use">Basic Use</link> |
  <link linkend="format_strings">Format Strings</link> |
  <link linkend="content_strings">Content Strings</link> |
  <link linkend="tut_sv">Special Values</link> |
  <link linkend="tut_dper">Date/Time Periods</link> |
  <link linkend="tut_dgen">Date Generators</link>
  
  <anchor id="basic_use" />
  <bridgehead renderas="sect4">Basic Use</bridgehead>
  <para>Facets are automatically imbued when operators '>>' and '&lt;&lt;' are called. The list of date_time objects that can be streamed are:</para>
  <bridgehead renderas="sect5">Gregorian</bridgehead>
  <para>
    <code>date</code>, 
    <code>days</code>, 
    <code>date_period</code>, 
    <code>greg_month</code>, 
    <code>greg_weekday</code>, 
    <code>greg_year</code>, 
    <code>partial_date</code>, 
    <code>nth_day_of_the_week_in_month</code>, 
    <code>first_day_of_the_week_in_month</code>, 
    <code>last_day_of_the_week_in_month</code>, 
    <code>first_day_of_the_week_after</code>, 
    <code>first_day_of_the_week_before</code>
  </para>
  <bridgehead renderas="sect5">Posix_time</bridgehead>
  <para>
    <code>ptime</code>, 
    <code>time_period</code>, 
    <code>time_duration</code>
  </para>
  <bridgehead renderas="sect5">Local_time</bridgehead>
  <para>
    <code>local_date_time</code>
  </para>
  
  <para>
    The following example is of the basic use of the new IO code, utilizing all the defaults. (this example can be found in the <code>libs/date_time/examples/tutorial</code> directory)
  </para>
  <programlisting>
    <![CDATA[
  date d(2004, Feb, 29);
  time_duration td(12,34,56,789);
  stringstream ss;
  ss << d << ' ' << td;
  ptime pt(not_a_date_time);
  cout << pt << endl; // "not-a-date-time"
  ss >> pt;
  cout << pt << endl; // "2004-Feb-29 12:34:56.000789"
  ss.str("");
  ss << pt << " EDT-05EDT,M4.1.0,M10.5.0";
  local_date_time ldt(not_a_date_time);
  ss >> ldt;
  cout << ldt << endl; // "2004-Feb-29 12:34:56.000789 EDT"
    ]]>
  </programlisting>

  <para>This example used the default settings for the input and output facets. The default formats are such that interoperability like that shown in the example is possible. NOTE: Input streaming of local_date_time can only be done with a <link linkend="date_time.local_time.posix_time_zone">posix time zone string</link>. The default output format uses a time zone abbreviation. The format can be changed so out and in match (as we will see later in this tutorial).</para>

  <anchor id="format_strings" />
  <bridgehead renderas="sect4">Format Strings</bridgehead>
  <para>The format strings control the order, type, and style of the date/time elements used. The facets provide some predefined formats (iso_format_specifier, iso_format_extended_specifier, and default_date_format) but the user can easily create their own.</para>
  (continued from previous example)
  <programlisting>
    <![CDATA[
  local_time_facet* output_facet = new local_time_facet();
  local_time_input_facet* input_facet = new local_time_input_facet();
  ss.imbue(locale(locale::classic(), output_facet));
  ss.imbue(locale(ss.getloc(), input_facet));
  
  output_facet->format("%a %b %d, %H:%M %z");
  ss.str("");
  ss << ldt;
  cout << ss.str() << endl; // "Sun Feb 29, 12:34 EDT"

  output_facet->format(local_time_facet::iso_time_format_specifier);
  ss.str("");
  ss << ldt;
  cout << ss.str() << endl; // "20040229T123456.000789-0500"
 
  output_facet->format(local_time_facet::iso_time_format_extended_specifier);
  ss.str("");
  ss << ldt;
  cout << ss.str() << endl; // "2004-02-29 12:34:56.000789-05:00"
    ]]>
  </programlisting>

  <para>Format strings are not limited to date/time elements. Extra verbiage can be placed in a format string. NOTE: When extra verbiage is present in an input format, the data being input must also contain the exact verbiage.</para>
  (continued from previous example)
  <programlisting>
    <![CDATA[
  // extra words in format
  string my_format("The extended ordinal time %Y-%jT%H:%M can also be \
  represented as %A %B %d, %Y");
  output_facet->format(my_format.c_str());
  input_facet->format(my_format.c_str());
  ss.str("");
  ss << ldt;
  cout << ss.str() << endl;

  // matching extra words in input 
  ss.str("The extended ordinal time 2005-128T12:15 can also be \
  represented as Sunday May 08, 2005");
  ss >> ldt;
  cout << ldt << endl;
    ]]>
  </programlisting>

  <anchor id="content_strings" />
  <bridgehead renderas="sect4">Content Strings</bridgehead>
  <para>So far we've shown how a user can achieve a great deal of customization with very little effort by using formats. Further customization can be achieved through user defined elements (ie strings). The elements that can be customized are: Special value names, month names, month abbreviations, weekday names, weekday abbreviations, delimiters of the date/time periods, and the phrase elements of the date_generators.</para>
  <para>The default values for these are as follows:</para>
  <bridgehead renderas="sect5">Special values</bridgehead>
  <para>
    <code>not-a-date-time</code>, 
    <code>-infinity</code>, 
    <code>+infinity</code>, 
    <code>minimum-date-time</code>, 
    <code>maximum-date-time</code>
  </para>
  <bridgehead renderas="sect5">Months</bridgehead>
  <para>
    <code>English calendar and three letter abbreviations</code>
  </para>
  <bridgehead renderas="sect5">Weekdays</bridgehead>
  <para>
    <code>English calendar and three letter abbreviations</code>
  </para>
  <bridgehead renderas="sect5">Date generator phrase elements</bridgehead>
  <para>
    <code>first</code>, 
    <code>second</code>, 
    <code>third</code>, 
    <code>fourth</code>, 
    <code>fifth</code>, 
    <code>last</code>, 
    <code>before</code>, 
    <code>after</code>, 
    <code>of</code>
  </para>
  <para>NOTE: We've shown earlier that the components of a date/time representation can be re-ordered via the format string. This is not the case with date_generators. The elements themselves can be customized but their order cannot be changed.</para>

  <bridgehead renderas="sect4">Content Strings</bridgehead>
  <para>To illustrate the customization possibilities we will use custom strings for months and weekdays (we will only use long names, is all lowercase, for this example).</para>
  (continued from previous example)
  <programlisting>
    <![CDATA[
  // set up the collections of custom strings.
  // only the full names are altered for the sake of brevity
  string month_names[12] = { "january", "february", "march", 
                             "april", "may", "june", 
                             "july", "august", "september", 
                             "october", "november", "december" };
  vector<string> long_months(&month_names[0], &month_names[12]);
  string day_names[7] = { "sunday", "monday", "tuesday", "wednesday", 
                          "thursday", "friday", "saturday" };
  vector<string> long_days(&day_names[0], &day_names[7]);
  
  //  create date_facet and date_input_facet using all defaults
  date_facet* date_output = new date_facet();
  date_input_facet* date_input = new date_input_facet();
  ss.imbue(locale(ss.getloc(), date_output)); 
  ss.imbue(locale(ss.getloc(), date_input));

  // replace names in the output facet
  date_output->long_month_names(long_months);
  date_output->long_weekday_names(long_days);
  
  // replace names in the input facet
  date_input->long_month_names(long_months);
  date_input->long_weekday_names(long_days);
  
  // customize month, weekday and date formats
  date_output->format("%Y-%B-%d");
  date_input->format("%Y-%B-%d");
  date_output->month_format("%B"); // full name
  date_input->month_format("%B"); // full name
  date_output->weekday_format("%A"); // full name
  date_input->weekday_format("%A"); // full name

  ss.str("");
  ss << greg_month(3);
  cout << ss.str() << endl; // "march"
  ss.str("");
  ss << greg_weekday(3);
  cout << ss.str() << endl; // "tuesday"
  ss.str("");
  ss << date(2005,Jul,4);
  cout << ss.str() << endl; // "2005-july-04"
    ]]>
  </programlisting>


  <anchor id="tut_sv" />
  <bridgehead renderas="sect4">Special Values</bridgehead>
  <para>Customizing the input and output of special values is best done by creating a new special_values_parser and special_values_formatter. The new strings can be set at construction time (as in the example below).</para>
  (continued from previous example)
  <programlisting>
    <![CDATA[
  // reset the formats to defaults
  output_facet->format(local_time_facet::default_time_format);
  input_facet->format(local_time_input_facet::default_time_input_format);

  // create custom special_values parser and formatter objects
  // and add them to the facets
  string sv[5] = {"nadt","neg_inf", "pos_inf", "min_dt", "max_dt" };
  vector<string> sv_names(&sv[0], &sv[5]);
  special_values_parser sv_parser(sv_names.begin(), sv_names.end());
  special_values_formatter sv_formatter(sv_names.begin(), sv_names.end());
  output_facet->special_values_formatter(sv_formatter);
  input_facet->special_values_parser(sv_parser);

  ss.str("");
  ldt = local_date_time(not_a_date_time);
  ss << ldt;
  cout << ss.str() << endl; // "nadt"
  
  ss.str("min_dt");
  ss >> ldt;
  ss.str("");
  ss << ldt;
  cout << ss.str() << endl; // "1400-Jan-01 00:00:00 UTC"
    ]]>
  </programlisting>
  <para>NOTE: even though we sent in strings for min and max to the formatter, they are ignored because those special values construct to actual dates (as shown above).</para>


  <anchor id="tut_dper" />
  <bridgehead renderas="sect4">Date/Time Periods</bridgehead>
  <para>Customizing the input and output of periods is best done by creating a new period_parser and period_formatter. The new strings can be set at construction time (as in the example below).</para>
  (continued from previous example)
  <programlisting>
    <![CDATA[
  // all formats set back to defaults (not shown for brevity)

  // create our date_period
  date_period dp(date(2005,Mar,1), days(31)); // month of march

  // custom period formatter and parser
  period_formatter per_formatter(period_formatter::AS_OPEN_RANGE, 
                                 " to ", "from ", " exclusive", " inclusive" );
  period_parser per_parser(period_parser::AS_OPEN_RANGE, 
                           " to ", "from ", " exclusive" , "inclusive" );
  
  // default output
  ss.str("");
  ss << dp;
  cout << ss.str() << endl; // "[2005-Mar-01/2005-Mar-31]"
 
  // add out custom parser and formatter to  the facets
  date_output->period_formatter(per_formatter);
  date_input->period_parser(per_parser);
  
  // custom output
  ss.str("");
  ss << dp;
  cout << ss.str() << endl; // "from 2005-Feb-01 to 2005-Apr-01 exclusive"
    ]]>
  </programlisting>

  <anchor id="tut_dgen" />
  <bridgehead renderas="sect4">Date Generators</bridgehead>
  <para>Customizing the input and output of date_generators is done by replacing the existing strings (in the facet) with new strings.</para>
  <para>NOTE: We've shown earlier that the components of a date/time representation can be re-ordered via the format string. This is not the case with date_generators. The elements themselves can be customized but their order cannot be changed.</para>
  (continued from previous example)
  <programlisting>
    <![CDATA[
  // custom date_generator phrases
  string dg_phrases[9] = { "1st", "2nd", "3rd", "4th", "5th", 
                           "final", "prior to", "following", "in" };
  vector<string> phrases(&dg_phrases[0], &dg_phrases[9]);

  // create our date_generator
  first_day_of_the_week_before d_gen(Monday);

  // default output
  ss.str("");
  ss << d_gen;
  cout << ss.str() << endl; // "Mon before"
 
  // add our custom strings to the date facets
  date_output->date_gen_phrase_strings(phrases);
  date_input->date_gen_element_strings(phrases);
  
  // custom output
  ss.str("");
  ss << d_gen;
  cout << ss.str() << endl; // "Mon prior to"
    ]]>
  </programlisting>

</section>