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| <h4 class="subsection">21.4.8 Functions and Variables for Time Zones</h4> |
| |
| <!-- time.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Variable: char * <b>tzname</b> [<var>2</var>]<var><a name="index-tzname-2674"></a></var><br> |
| <blockquote><p>The array <code>tzname</code> contains two strings, which are the standard |
| names of the pair of time zones (standard and Daylight |
| Saving) that the user has selected. <code>tzname[0]</code> is the name of |
| the standard time zone (for example, <code>"EST"</code>), and <code>tzname[1]</code> |
| is the name for the time zone when Daylight Saving Time is in use (for |
| example, <code>"EDT"</code>). These correspond to the <var>std</var> and <var>dst</var> |
| strings (respectively) from the <code>TZ</code> environment variable. If |
| Daylight Saving Time is never used, <code>tzname[1]</code> is the empty string. |
| |
| <p>The <code>tzname</code> array is initialized from the <code>TZ</code> environment |
| variable whenever <code>tzset</code>, <code>ctime</code>, <code>strftime</code>, |
| <code>mktime</code>, or <code>localtime</code> is called. If multiple abbreviations |
| have been used (e.g. <code>"EWT"</code> and <code>"EDT"</code> for U.S. Eastern War |
| Time and Eastern Daylight Time), the array contains the most recent |
| abbreviation. |
| |
| <p>The <code>tzname</code> array is required for POSIX.1 compatibility, but in |
| GNU programs it is better to use the <code>tm_zone</code> member of the |
| broken-down time structure, since <code>tm_zone</code> reports the correct |
| abbreviation even when it is not the latest one. |
| |
| <p>Though the strings are declared as <code>char *</code> the user must refrain |
| from modifying these strings. Modifying the strings will almost certainly |
| lead to trouble. |
| |
| </blockquote></div> |
| |
| <!-- time.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Function: void <b>tzset</b> (<var>void</var>)<var><a name="index-tzset-2675"></a></var><br> |
| <blockquote><p>The <code>tzset</code> function initializes the <code>tzname</code> variable from |
| the value of the <code>TZ</code> environment variable. It is not usually |
| necessary for your program to call this function, because it is called |
| automatically when you use the other time conversion functions that |
| depend on the time zone. |
| </p></blockquote></div> |
| |
| <p>The following variables are defined for compatibility with System V |
| Unix. Like <code>tzname</code>, these variables are set by calling |
| <code>tzset</code> or the other time conversion functions. |
| |
| <!-- time.h --> |
| <!-- SVID --> |
| <div class="defun"> |
| — Variable: long int <b>timezone</b><var><a name="index-timezone-2676"></a></var><br> |
| <blockquote><p>This contains the difference between UTC and the latest local standard |
| time, in seconds west of UTC. For example, in the U.S. Eastern time |
| zone, the value is <code>5*60*60</code>. Unlike the <code>tm_gmtoff</code> member |
| of the broken-down time structure, this value is not adjusted for |
| daylight saving, and its sign is reversed. In GNU programs it is better |
| to use <code>tm_gmtoff</code>, since it contains the correct offset even when |
| it is not the latest one. |
| </p></blockquote></div> |
| |
| <!-- time.h --> |
| <!-- SVID --> |
| <div class="defun"> |
| — Variable: int <b>daylight</b><var><a name="index-daylight-2677"></a></var><br> |
| <blockquote><p>This variable has a nonzero value if Daylight Saving Time rules apply. |
| A nonzero value does not necessarily mean that Daylight Saving Time is |
| now in effect; it means only that Daylight Saving Time is sometimes in |
| effect. |
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