/usr/share/doc/libbobcat2-dev/man/datetime.3.html

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<title>FBB::DateTime</title>
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<h1>FBB::DateTime</h1>
<h2>libbobcat1-dev_2.20.01-x.tar.gz</h2>
<h2>2005-2011</h2>

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<html><head>
<title>FBB::DateTime(3bobcat)</title>
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<h1>FBB::DateTime(3bobcat)</h1>
<h2>libbobcat1-dev_2.20.01-x.tar.gz Date and Time</h2>
<h2>2005-2011</h2>


<p>
<h2>NAME</h2>FBB::DateTime - Performs Date and Time Computations
<p>
<h2>SYNOPSIS</h2>
    <strong>#include &lt;bobcat/datetime&gt;</strong><br>
    Linking option: <em>-lbobcat</em> 
<p>
<h2>DESCRIPTION</h2>
<p>
This class allows the programmer to manipulate date and time
values. Individual time fields can be requested or modified, returning
`sanitized' times (e.g., a date like march 33 or a time like 56 hours will
never be returned). Times may be specified in local time or in <em>Universal
Time Coordinated</em> (<em>UTC</em>) values. It is also possible to add or subtract
seconds or <strong>struct tm</strong> structures to or from <em>DateTime</em> objects. This
operation keeps the current time zone (<em>UTC</em>, local or another time
zone). Conversions between time zones and <em>UTC</em> are also supported.
<p>
The class <em>DateTime</em> supports various ways to initialize objects. Time may
be specified in UTC, as local time or using any other offset from UTC. When an
explicit time offset is requested it is specified as an <em>int</em> value
representing the time offset in minutes, with time zones time zones West of
Greenwich using negative time offsets and East of Greenwich using positive
time offsets. Time zone offsets are truncated to multiples of 30 minutes and
are always computed modulo 12 * 60, as no time zone has a shift exceeding the
(absolute) shift of 12 * 60. Daylight saving times are in effect in many time
zones. Except for the local time zone <em>DateTime</em> may not be able to show the
correct daylight saving time correction.
<p>
There are various ways to construct <em>DateTime</em> objects: time in seconds
since the beginning of the `era' (midnight Jan 1, 1970 UTC), a <em>struct tm</em>,
or a textual time representations may be used. These values may themselves be
corrected using display zone shifts. A display zone shift determines the
difference between the UTC time and the local time zone to be used when
displaying time or returning time fields.  Sometimes a UTC zone shift may be
provided correcting a provided local time to UTC. 
<p>
If a display zone shift is explicitly specified no additional daylight saving
time (DST) zone shift is added to the display time. If the actual local time
is requested (specified by the <em>TimeType</em> value <em>LOCALTIME</em>) a DST
correction is automatically applied when appropriate.
<p>
Members of the class <em>DateTime</em> should only be used if <em>operator bool()</em>
returns <em>true</em>. The member <em>error()</em> can also be used if <em>operator
bool()</em> returns false.
<p>
Handling time is complex. The <strong>C</strong> function <strong>time</strong>(2) returns the time in
seconds. This time is normally represented in UTC. The function <strong>gmtime</strong>(3)
when provided with <em>time()</em>'s output returns the broken down time in a
<em>struct tm</em>. Remarkably (and confusingly), when this <em>struct tm</em> is then
passed to the <strong>mktime</strong>(3) function the latter function does <em>not</em> return
the UTC-time in seconds, but a time that differs from the time in UTC by the
current local time shift. E.g., the program
        <pre>
    #include &lt;ctime&gt;
    #include &lt;iostream&gt;
    using namespace std;

    int main()
    {
        time_t utc = time(0);
        struct tm *ts;
        time_t local = mktime(ts = gmtime(&amp;utc));
        
        cout &lt;&lt; ts-&gt;tm_hour &lt;&lt; ' ' &lt;&lt; utc - local &lt;&lt; endl;
        return 0;
    }
</pre>

    displays the current <em>UTC</em> clock's hour setting, but reports the
difference in seconds between the local time and the UTC time (e.g., the
difference between CET and UTC is one hour, and the program displays 3600).
<p>
To obtain the time in UTC-seconds from <em>mktime</em>(3) the function
<strong>localtime</strong>(3) must be used to obtain the <em>struct tm</em> values:
        <pre>
    #include &lt;ctime&gt;
    #include &lt;iostream&gt;
    using namespace std;

    int main()
    {
        time_t utc = time(0);
        struct tm *ts;
        time_t local = mktime(ts = localtime(&amp;utc));
        
        cout &lt;&lt; ts-&gt;tm_hour &lt;&lt; ' ' &lt;&lt; utc - local &lt;&lt; endl;
        return 0;
    }
</pre>

    The above program displays the local clock's hour value, but a difference
of 0 for the recomputed time in seconds. 
<p>
The class <em>DateTime</em> assumes that the <em>time()</em> function returns the UTC
time in seconds, which is the way computers should have configured their
hardware clock. 
<p>
<h2>NAMESPACE</h2>
    <strong>FBB</strong><br>
    All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace <strong>FBB</strong>.
<p>
<h2>INHERITS FROM</h2>    
    -
<p>
<h2>ENUMS defined in DateTime</h2>
<p>
<strong>DateTime::Month</strong><br>
    This enumeration has the following values which are ordered using the
default <strong>C++</strong> <em>enum</em> values:
    <ul>
    <li> <strong>JANUARY</strong>,
    <li> <strong>FEBRUARY</strong>,
    <li> <strong>MARCH</strong>,
    <li> <strong>APRIL</strong>,
    <li> <strong>MAY</strong>,
    <li> <strong>JUNE</strong>,
    <li> <strong>JULY</strong>,
    <li> <strong>AUGUST</strong>,
    <li> <strong>SEPTEMBER</strong>,
    <li> <strong>OCTOBER</strong>,
    <li> <strong>NOVEMBER</strong>,
    <li> <strong>DECEMBER</strong>.
    </ul>
<p>
<strong>DateTime::Relative</strong><br>
    This enumeration is used with the <em>setMonth()</em> member (see below).
    It has the following values:
    <ul>
    <li> <strong>THIS_WEEK</strong>,
    <li> <strong>THIS_YEAR</strong>,
    <li> <strong>LAST</strong>,
    <li> <strong>NEXT</strong>
    </ul>
<p>
<strong>DateTime::TimeFields</strong><br>
    This enumeration has the following values which can be <em>bit_or</em>-ed
    when calling the member <em>setFields()</em>:
    <ul>
    <li> <strong>SECONDS</strong>
    <li> <strong>MINUTES</strong>
    <li> <strong>HOURS</strong>
    <li> <strong>MONTHDAY</strong>
    <li> <strong>MONTH</strong>
    <li> <strong>YEAR</strong>
    </ul>
<p>
<strong>DateTime::TimeType</strong><br>
    This enumeration has the following values:
    <ul>
    <li> <strong>LOCALTIME</strong>: the time is broken down  as the local time,
    <li> <strong>UTC</strong>: the time is broken down as Universal Time Coordinated.
    </ul>
<p>
<strong>DateTime::TriVal</strong><br>
    This enumeration has the following values, returned by the <strong>dst()</strong>
    member (see below): 
    <ul>
    <li> <strong>UNKNOWN</strong>, returned when no information about the Daylight
        Saving Time is available,
    <li> <strong>NO</strong>, returned when Daylight Saving Time is not active,
    <li> <strong>YES</strong>, returned when Daylight Saving Time is active.
    </ul>
<p>
<strong>DateTime::Weekday</strong><br>
    This enumeration has the following values which are ordered using the
default <strong>C++</strong> <em>enum</em> values:
<p>
<ul>
    <li> <strong>SUNDAY</strong>,
    <li> <strong>MONDAY</strong>,
    <li> <strong>TUESDAY</strong>,
    <li> <strong>WEDNESDAY</strong>,
    <li> <strong>THURSDAY</strong>,
    <li> <strong>FRIDAY</strong>,
    <li> <strong>SATURDAY</strong>.
    </ul>
<p>
<h2>STANDARD TEXTUAL TIME REPRESENTATIONS</h2>    
<p>
<em>DateTime</em> objects may be initialized using textual
time-representations. Also, the time represented by a <em>DateTime</em> object may
be altered using text which can be extracted from a stream using 
the extraction operator.
<p>
Time specifications may be formatted as follows:
    <ul>
    <li> <em>Sun Nov 2 13:29:11 2008</em>, as displayed by the <strong>C</strong> function
<em>asctime()</em>;
<p>
<li> <em>Sun Nov 2 13:29:11 CET 2008</em>, as displayed by the <strong>date</strong>(1) program;
<p>
<li> <em>Sun, Nov 2 13:29:11 2008 +0100</em>, as displayed by the <em>date -R</em>
command (and the <em>rfc2822()</em> member, see below);
<p>
<li> <em>2008-11-02 13:29:11+01:00</em>, as displayed by the <em>date
--rfc-3339=seconds</em> command (and the <em>rfc3339()</em> member, see below).
    </ul>
<p>
The time zone time shift specifications (+0100, +01:00) are required as they
are part of the rfc specifications but are ignored for the actual local time
construction as the <em>DateTime</em> object determines the time zone specification
from the computer's current time zone setting.
<p>
<h2>CONSTRUCTORS</h2>
<p>
<ul>
    <li> <strong>DateTime(TimeType type = UTC)</strong>:<br>
        The default constructor, initializing the object to the current date
and time.  The argument specifies the way the time is displayed by the
<em>DateTime</em> object using either (by default) time in UTC or the computer's
time zone shift is used to determine the current local time.
<p>
<li> <strong>DateTime(int tzShift)</strong>:<br>
        This constructor initializes the object to a local time which is at
UTC + tzShift (in minutes).
<p>
<li> <strong>DateTime(time_t time, TimeType type)</strong>:<br>
        Initializes a <em>DateTime</em> object with information stored in the
provided <em>time_t</em> value (time in seconds since the beginning of the era). 
The specified <em>time</em> is considered UTC or local time, depending on the
<em>type</em> specification.
<p>
<li> <strong>DateTime(time_t time, int tzShift)</strong>:<br>
        Initializes a <em>DateTime</em> object with information stored in the
provided <em>time_t</em> value (time is UTC time in seconds since the beginning of
the era). The <em>DateTime</em> object defines its time as local time UTC + tzShift
(in minutes).
    </ul>
<p>
The following constructors ignore the DST, day of the year, and day of the
week fields of the <em>struct tm</em> passed to the constructors:
<p>
<ul>
    <li> <strong>DateTime(struct tm const &amp;tm, TimeType type = UTC)</strong>:<br>
        Initializes a <em>DateTime</em> object with information stored in the
provided <strong>struct tm</strong> value. It is assumed that the <em>tm</em> parameter points
to a <em>struct tm</em> representing the broken down time in either UTC or local
time. If local time is requested the the computer's time zone shift is
used. The <strong>struct tm</strong> is defined as follows:
        <pre>

struct tm 
{
    int tm_sec;     // seconds          0..59, or 60: leap second
    int tm_min;     // minutes          0..59
    int tm_hour;    // hours            0..23
    int tm_mday;    // day of the month 1..31
    int tm_mon;     // month            0..11
    int tm_year;    // year             since 1900
    int tm_wday;    // day of the week  0..6
    int tm_yday;    // day in the year  0..365
    int tm_isdst;   // daylight saving time
                    // &gt; 0: yes, 0: no, &lt; 0: unknown
};
        
</pre>

    Values outside of these ranges may sometimes be used (with various
set..() members, see below) to compute a point in time in the future or in the
past. E.g., by specifying 30 for the hour-setting <strong>DateTime</strong> objects 
a point in time in the next day will be used.
<p>
<li> <strong>DateTime(struct tm const &amp;tm, int timeShift)</strong>:<br>
        Initializes a <em>DateTime</em> object with information stored in the
provided <strong>struct tm</strong> value. It is assumed that the <em>tm</em> parameter points
to a <em>struct tm</em> representing the broken down time fields in UTC. To this
time shift <em>tzShift</em> (in minutes) is added to obtain the actually used
local time.
    </ul>
<p>
The final constructors convert textual time specifications formatted as
described in section <strong>STANDARD TEXTUAL TIME REPRESENTATIONS</strong> (the day of the
week specification is ignored by the time conversion).
<p>
<ul>
    <li> <strong>DateTime(std::string const &amp;timeStr, TimeType type = UTC)</strong>:<br>
        Initializes a <em>DateTime</em> object with information stored in the
provided <em>std::string</em> which is interpreted as time specified in UTC or as a
local time in the current time zone, depending on the specified time type.
<p>
<li> <strong>DateTime(std::string const &amp;timeStr, int tzShift)</strong>:<br>
        Initializes a <em>DateTime</em> object with a local time computed by adding
a locate timezone shift (<em>tzShift</em>) in minutes to  the UTC time
specification found in <em>timeStr</em>.
    </ul>
<p>
The copy constructor is available.
<p>
<h2>OVERLOADED OPERATORS</h2>
<p>
All class-less overloaded operators are defined in the <em>FBB</em> namespace,
except for the overloaded insertion operator, which is defined in the <em>std</em>
namespace. 
<p>
<ul>
    <li> <strong>std::ostream &amp;std::operator&lt;&lt;(std::ostream &amp;str, FBB::DateTime 
        const &amp;dt)</strong>:<br>
        Inserts a standard textual representation (without the trailing
newline), of the time represented in the <em>DateTime</em> object into the
indicated <em>ostream</em>. The time will be displayed according to the latest
<em>displayZoneShift</em> or <em>TimeType</em> specification (<em>LOCALTIME</em> or <em>UTC</em>).
<p>
<li> <strong>std::istream &amp;std::operator&gt;&gt;(std::istream &amp;str, FBB::DateTime &amp;dt)</strong>:<br>
        Extracts a textual date/time representation into the <em>DateTime</em>
object using the <em>tzShift</em> value currently set for the <em>DateTime</em> object
into which the time string is extracted.
<p>
The <em>istream</em> from which the time is extracted must contain time
formatted as described in section <strong>STANDARD TEXTUAL TIME
REPRESENTATIONS</strong>. As documented in that section, time shift and time zone
specifications (+0100, +01:00, CET) are ignored and may be omitted.  They are
ignored when specified. The object will merely interpret the date/time
specification as a specification in the object's currently active time zone.
<p>
If the time could not be determined from a textual string representing the
time (cf. section <strong>CONSTRUCTORS</strong>) then  <em>errno()</em> returns 0,
<em>operator bool()</em> returns <em>false</em>, and the time stored in the object 
remains unchanged. 
    </ul>
<p>
The following overloaded operators modify the time as stored in UTC
seconds within objects. Note that the time as displayed by the object will be
corrected for any display zone shift that may have been defined for those
objects.
<p>
<ul>
    <li> <strong>DateTime const operator+(DateTime const &amp;left, time_t seconds)</strong>:<br>
       Returns a copy of <em>left</em> to which <em>seconds</em> have been added.
<p>
<li> <strong>DateTime const operator+(DateTime const &amp;left, 
                                            struct tm const &amp;fields)</strong>:<br>
        Returns a copy of <em>left</em> displaying <em>left</em>'s time to which the
<em>tm_sec, tm_min, tm_hour, tm_mday, tm_mon</em> and <em>tm_year</em> fields of
<em>fields</em> have been added.
<p>
<li> <strong>DateTime operator+=(time_t seconds)</strong>:<br>
       Adds the number of seconds to the <em>DateTime</em> object.
<p>
<li> <strong>DateTime &amp;operator+=(struct tm const &amp;fields)</strong>:<br>
        Adds the <em>tm_sec, tm_min, tm_hour, tm_mday, tm_mon</em> and <em>tm_year</em>
fields of <em>fields</em>to the current object's display time.
<p>
<li> <strong>DateTime const operator-(DateTime const &amp;left, time_t seconds)</strong>:<br>
       Returns a copy of <em>left</em> from which time <em>seconds</em> have been
subtracted. 
<p>
<li> <strong>DateTime const operator-(DateTime const &amp;left, 
                                struct tm const &amp;fields)</strong>:<br>
        Returns a copy of <em>left</em> displaying <em>left</em>'s time from which the
<em>tm_sec, tm_min, tm_hour, tm_mday, tm_mon</em> and <em>tm_year</em> fields of
<em>fields</em> have been subtracted.
<p>
<li> <strong>DateTime operator-=(time_t seconds)</strong>:<br>
       Subtracts the number of seconds from the time stored in the
<em>DateTime</em> object.
<p>
<li> <strong>DateTime &amp;operator-=(struct tm const &amp;fields)</strong>:<br>
        Subtracts the <em>tm_sec, tm_min, tm_hour, tm_mday, tm_mon</em> and
<em>tm_year</em> fields of <em>fields</em> from the current object's display time.
E.g., the following
code fragment will display midnight, January 1, 1970:
        <pre>
time_t seconds = time(0);
tm timeStruct = *gmtime(&amp;seconds);

DateTime tmp(timeStruct);
cout &lt;&lt; tmp &lt;&lt; endl;

--timeStruct.tm_mday;       // days start at 1: subtract 1 less than
                            // the current day number to get '01'

timeStruct.tm_year -= (1970 - 1900);    // era starts at 1970, tm_year
                                        // is relative to 1900.

tmp -= timeStruct;
cout &lt;&lt; tmp &lt;&lt; endl;
</pre>

    </ul>
<p>
The following overloaded operators can be used to compare the UTC time as
represented by <em>DateTime</em> objects. Note that these comparisons are
independent of any display zone shift that may have been defined for the
objects.
<p>
<ul>
    <li> <strong>bool operator==(DateTime const &amp;left, DateTime const &amp;right)</strong>:<br>
       Returns <em>true</em> if the current <em>DateTime</em> object represents the same
UTC time as the time represented by <em>left, DateTime const &amp;right</em>.
<p>
<li> <strong>bool operator!=(DateTime const &amp;left, DateTime const &amp;right)</strong>:<br>
       Returns <em>true</em> if the current <em>DateTime</em> object represents a
different UTC time as the time represented by <em>other</em>.
<p>
<li> <strong>bool operator&lt;(DateTime const &amp;left, DateTime const &amp;right)</strong>:<br>
       Returns <em>true</em> if the current <em>DateTime</em> object represents an
earlier UTC time than the UTC time represented by <em>other</em>.
<p>
<li> <strong>bool operator&lt;=(DateTime const &amp;left, DateTime const &amp;right)</strong>:<br>
       Returns <em>true</em> if the current <em>DateTime</em> object represents an
earlier or equal UTC time than the UTC time represented by <em>other</em>.
<p>
<li> <strong>bool operator&gt;(DateTime const &amp;left, DateTime const &amp;right)</strong>:<br>
       Returns <em>true</em> if the current <em>DateTime</em> object represents a
later UTC time than the UTC time represented by <em>other</em>.
<p>
<li> <strong>bool operator&gt;=(DateTime const &amp;left, DateTime const &amp;right)</strong>:<br>
       Returns <em>true</em> if the current <em>DateTime</em> object represents an
equal or later UTC time than the UTC time represented by <em>other</em>.
    </ul>
<p>
Additional overloaded operators:
<p>
<ul>
    <li> <strong>operator bool() const</strong>:<br>
        Returns <strong>true</strong> if the time decomposition could be performed without
error. <em>DateTime</em> object use <strong>localtime_r</strong>(3) or <strong>gmtime_r</strong>(3)
functions to break down the <em>time_t</em> values into elements.  If the time
could not be broken down, the <strong>error()</strong> member returns the error number
(<em>errno</em>) associated with the error. When the time could not be determined
from a textual string representing the time (cf. section <strong>CONSTRUCTORS</strong>)
then <em>errno()</em> returns 0 and <em>operator bool()</em> returns <em>false</em>.<br>
    Except for the member <em>error()</em> the members of the class <em>DateTime</em>
will not return meaningfull values if <strong>operator bool()</strong> returns
<em>false</em>. 
<p>
<li> <strong>DateTime &amp;operator=(DateTime const &amp;other)</strong>:<br>
        The overloaded asignment operator is available.
    </ul>
<p>
<h2>MEMBER FUNCTIONS</h2>
<p>
All members returning a time-element do so according to the latest
time-representation (i.e., <em>UTC</em>, <em>LOCALTIME</em>, or using an explicitly set
display zone shift value). All members returning numerical values use 0 as
their smallest return value, except for the <strong>...Nr()</strong> members, which start
at 1.
    <ul>
    <li> <strong>int displayZoneShift() const</strong>:<br>
        Returns the object's current display zone shift value in minutes.
<p>
<li> <strong>DayTime::TriVal dst() const</strong>:<br>
        Returns an indication of an active Daylight Saving Time (DST) state
for the (local) time represented in the <em>DateTime</em> object. When DST is
active, the local time is one hour later as compared to the situation where
DST is not active.
<p>
<li> <strong>size_t error() const</strong>:<br>
        Returns the <em>errno</em> value after the <em>DateTime</em> object. 
construction.  It can be interpreted by, e.g., <strong>FBB::Errno</strong>.
<p>
<li> <strong>size_t hours() const</strong>:<br>
        Returns the number of hours of the time stored in a <em>DateTime</em>
object (0-23).
<p>
<li> <strong>DateTime localTime() const</strong>:<br>
        Returns a copy of the <em>DateTime</em> object representing its local
time. If the object does not define a local time or display zone shift the
returned object merely copies the orginal object's UTC time.
<p>
<li> <strong>DateTime localTime(int displayZoneShift) const</strong>:<br>
        Returns a copy of the <em>DateTime</em> object representing its time using
the display zone shift provided by the member's argument.
<p>
<li> <strong>size_t minutes() const</strong>:<br>
        Returns the number of minutes of the time stored in a <em>DateTime</em>
object (0-59).
<p>
<li> <strong>Month month() const</strong>:<br>
        Returns the <em>Month</em> value of the time stored in a <em>DateTime</em>
object.
<p>
<li> <strong>size_t monthDayNr() const</strong>:<br>
        Returns the number of the day in the month of the time stored in a
<em>DateTime</em> object (1-31).
<p>
<li> <strong>string rfc2822() const</strong>:<br>
        Returns the date displayed according to the format specified in RFC
2822. This format is used, e.g., by the <em>date -R</em> command
(cf. <strong>date</strong>(1)). For example:
        <pre>

        Mon, 17 Dec 2007 13:49:10 +0100
        
</pre>

<p>
<li> <strong>string rfc3339() const</strong>:<br>
        Returns the date displayed according to the format specified in RFC
3339. This format is used, e.g., by the <em>date --rfc-3339=seconds</em> command
(cf. <strong>date</strong>(1)). For example:
        <pre>

        2008-11-02 13:29:11+01:00
        
</pre>

<p>
<li> <strong>size_t seconds() const</strong>:<br>
        Returns the number of seconds of the time stored in a <em>DateTime</em>
object (0-59, but 60 and 61 may occur due to possible leap seconds).
<p>
<li> <strong>bool setDay(int days)</strong>:<br>
        Reassigns the number of days of the current month set in the
<em>DateTime</em> object. Non positive values are allowed to compute time in an
earlier month. The object date is revalidated so that its <em>days()</em>
member returns a value fitting the object's month. If the assignment resulted
in a new (valid) time <em>true</em> is returned. Otherwise <em>false</em> is returned.
<p>
<li> <strong>bool setFields(struct tm const &amp;timeStruct, int fields)</strong>:<br>
        Reassigns the time represented by the <em>DateTime</em> object to the time
in which the fields specified by a <em>bit_or</em> combination of <em>TimeField</em>
values will be given the values specified in <em>timeStruct</em>. All other fields
in <em>timeStruct</em> will be ignored and will be kept at their internal values.
The values will be normalized, though. E.g., if the current month day number
is 31 and month June is requested then the resulting month will be <em>July</em>
and the day number will be 1. The <em>timeStruct</em> fields are expected as values
in the time zone used by the <em>DateTime</em> object.  If the assignment resulted
in a new (valid) time <em>true</em> is returned. Otherwise <em>false</em> is returned.
<p>
<li> <strong>bool setHours(int hours)</strong>:<br>
        Reassigns the number of hours set in the <em>DateTime</em> object.
Negative values are allowed to compute time in a previous day. The object date
is revalidated so that its <em>hours()</em> member returns a value between 0 and
23. If the assignment resulted in a new (valid) time <em>true</em> is
returned. Otherwise <em>false</em> is returned.
<p>
<li> <strong>bool setMinutes(int minutes)</strong>:<br>
        Reassigns the number of minutes set in the <em>DateTime</em>
object. Negative values are allowed to compute time in a previous hour. The
object date is revalidated so that its <em>minutes()</em> member returns a value
between 0 and 59.  If the assignment resulted in a new (valid) time <em>true</em>
is returned. Otherwise <em>false</em> is returned.
<p>
<li> <strong>bool setMonth(DateTime::Month month, DateTime::Relative where =
            THIS_YEAR)</strong>:<br> 
        Reassigns the month set in the <em>DateTime</em> object. The object date is
revalidated so that its <em>month()</em> member returns a value between <em>JANUARY</em>
and <em>DECEMBER</em>. By default the month will be set in the current
year. <em>DateTime::LAST</em> may be specified to ensure that the requested month
will be before the current month (e.g., the current month: <em>JUNE</em>,
requesting <em>AUGUST, LAST</em> will decrement the object's year, but <em>MAY,
LAST</em> won't). Analogously, <em>DateTime::NEXT</em> may be specified to ensure that
the requested month will be following the current month. If another value for
<em>where</em> is specified an <strong>Errno</strong> exception is thrown. If the assignment
resulted in a new (valid) time <em>true</em> is returned. Otherwise <em>false</em> is
returned. 
<p>
Caveat: When setting the month the month may inadvertently be set to the
next month. This happens when the current day number exceeds the number of
days in the target month. Example: assume it is December 31st and the intent
is to change the date to June 21st. The first example sets the date to
<strong>July</strong> 21st since `June 31st' is converted to `July 1st'. The second example
sets the date to June 21st, as intended.
        <pre>

    DateTime dt;                    // assume set at December 31
    dt.setMonth(DateTime::JUNE);    // becomes JULY
    dt.setDay(21);                  // Now July 21st
    
    DateTime dt;                    // assume set at December 31
    dt.setDay(21);                  // Now December 21st
    dt.setMonth(DateTime::JUNE);    // OK: June 21st
        
</pre>

<p>
<li> <strong>bool setMonth(int month)</strong>:<br> 
        Reassigns the month set in the <em>DateTime</em> object. Negative values
are allowed to compute time in a previous year. The object date is revalidated
so that its <em>month()</em> member returns a value between <em>JANUARY</em> and
<em>DECEMBER</em>.  If the assignment resulted in a new (valid) time <em>true</em> is
returned. Otherwise <em>false</em> is returned.
<p>
<li> <strong>bool setSeconds(int seconds)</strong>:<br>
        Reassigns the number of seconds set in the <em>DateTime</em>
object. Negative values are allowed to compute time in a previous minute. The
object date is revalidated so that its <em>seconds()</em> member returns a value
between 0 and 59. If the assignment resulted in a new (valid) time <em>true</em> is
returned. Otherwise <em>false</em> is returned.
<p>
<li> <strong>bool setTime(time_t time)</strong>:<br>
        Reassigns the number of seconds set in the <em>DateTime</em> object. The
object date is revalidated. Time value 0 represents Jan, 1, 1970, 0:00:00
hours. If the assignment resulted in a new (valid) time <em>true</em> is
returned. Otherwise <em>false</em> is returned.
<p>
<li> <strong>void setValid()</strong>:<br>
        Resets the object's internal state to valid. This member can be used
following a failed action that did not modify the (valid) time stored 
by the object.
<p>
<li> <strong>bool setWeekday(Weekday day, Relative where = NEXT)</strong>:<br>
        Reassigns the number of seconds set in the <em>DateTime</em> object based
on reassignment of the day in the week (at most 7 days from now, weeks
starting at Sunday and ending at Saturday). By default the day will be in the
future. By specifying <em>LAST</em> for <em>where</em> the day will be in the past. It
is also possible to specify <em>where</em> as <em>THIS_WEEK</em> in which case the day
will be computed in the current week. If another value for <em>where</em> is
specified an <strong>Errno</strong> exception is thrown.  If the current weekday is
specified with <em>where</em> equal to either <em>NEXT</em> or <em>LAST</em> the time will be
set to either one week ahead or one week in the past. The object date is
revalidated. Time value 0 represents Jan, 1, 1970, 0:00:00 hours. If the
assignment resulted in a new (valid) time <em>true</em> is returned. Otherwise
<em>false</em> is returned.
<p>
<li> <strong>bool setYear(size_t year)</strong>:<br>
        Reassigns the year set in the <em>DateTime</em> object. The date is
revalidated so that its <em>year()</em> member returns a value of at least 1970. If
the assignment resulted in a new (valid) time <em>true</em> is returned. Otherwise
<em>false</em> is returned.
<p>
<li> <strong>time_t time() const</strong>:<br>
        Returns the (UTC) <em>time_t</em> value (in seconds) stored in the
<em>DateTime</em> object.
<p>
<li> <strong>struct tm const *timeStruct() const</strong>:<br>
        Returns a pointer to the objects latest <em>struct tm</em> values,
        representing the time as displayed by, e.g., the insertion operator.
<p>
<li> <strong>DateTime to(DateTime::TimeType type) const</strong>:<br>
        Returns a copy of the <em>DateTime</em> object representing its time in
        <em>UTC</em> if <em>DateTime::UTC</em> was specified, and in local time if
        <em>DateTime::LOCALTIME</em> was specified.
<p>
<li> <strong>DateTime utc() const</strong>:<br>
        Returns a copy of the <em>DateTime</em> object representing its time in
        <em>UTC</em>.
<p>
<li> <strong>bool valid() const</strong>:<br>
        Returns <em>true</em> if no errors were detected during the object's
        construction (same semantics as <em>operator bool()</em>).
<p>
<li> <strong>Weekday weekday() const</strong>:<br>
        Returns the <em>Weekday</em> value of the time stored in a
        <em>DateTime</em> object.
<p>
<li> <strong>size_t year() const</strong>:<br>
        Returns the year element of the time stored in a <em>DateTime</em>
        object.
<p>
<li> <strong>size_t yearDay() const</strong>:<br>
        Returns the day within the year of the time stored in a
<em>DateTime</em> object. January 1 is returned as 0.
<p>
<li> <strong>size_t yearDayNr() const</strong>:<br>
        Returns the day within the year of the time stored in a
        <em>DateTime</em> object. January 1 is returned as 1.
<p>
</ul>
    Whenever a <em>set...()</em> member is used in such a way that the resulting
date would be invalid the original <em>DateTime</em> object's value is unaltered.
<p>
<h2>EXAMPLE</h2>
<p>
An extensive example illustrating the use of all of <em>DateTime</em>'s members
is provided in the file <em>bobcat/datetime/driver/driver.cc</em> found in the
source archive.
<p>
<h2>FILES</h2>
    <em>bobcat/datetime</em> defines the class interface.
<p>
<h2>SEE ALSO</h2>
        <strong>bobcat</strong>(7), <strong>Errno</strong>(3bobcat), <strong>asctime_r</strong>(3), 
        <strong>gmtime_r</strong>(3), <strong>localtime_r</strong>(3), <strong>time</strong>(2),
        <strong>mktime</strong>(3),
<p>
<h2>BUGS</h2>
    The class <em>DateTime</em> assumes that <strong>time</strong>(2) returns the time in
    UTC.<br>
    English is used / expected when specifying named date components.
<p>

<h2>DISTRIBUTION FILES</h2>
    <ul>
    <li> <em>bobcat_2.20.01-x.dsc</em>: detached signature;
    <li> <em>bobcat_2.20.01-x.tar.gz</em>: source archive;
    <li> <em>bobcat_2.20.01-x_i386.changes</em>: change log;
    <li> <em>libbobcat1_2.20.01-x_*.deb</em>: debian package holding the
            libraries;
    <li> <em>libbobcat1-dev_2.20.01-x_*.deb</em>: debian package holding the
            libraries, headers and manual pages;
    <li> <em>http://sourceforge.net/projects/bobcat</em>: public archive location;
    </ul>
<p>
<h2>BOBCAT</h2>
    Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.
<p>
<h2>COPYRIGHT</h2>
    This is free software, distributed under the terms of the 
    GNU General Public License (GPL).
<p>
<h2>AUTHOR</h2>
    Frank B. Brokken (<strong>f.b.brokken@rug.nl</strong>).
<p>
libbobcat-dev 2.20.01-1 / usr / share / doc / libbobcat2-dev / man / datetime.3.html
