[Plplot-cvs] SF.net SVN: plplot:[8530] trunk/examples/c

[<ai...@us...>]

Revision: 8530
          http://plplot.svn.sourceforge.net/plplot/?rev=8530&view=rev
Author:   airwin
Date:     2008-07-18 17:40:06 +0000 (Fri, 18 Jul 2008)

Log Message:
-----------
Change to POSIX-compliant equivalent of timegm GNU extension.

Modified Paths:
--------------
    trunk/examples/c/x29c.c
    trunk/examples/c++/x29.cc

Modified: trunk/examples/c/x29c.c
===================================================================
--- trunk/examples/c/x29c.c	2008-07-18 17:24:42 UTC (rev 8529)
+++ trunk/examples/c/x29c.c	2008-07-18 17:40:06 UTC (rev 8530)
@@ -159,19 +159,16 @@
 {
   int i, npts;
   PLFLT xmin, xmax, ymin, ymax;
-  time_t t1, t2;
-  PLFLT tstart, toff;
+  PLFLT tstart;
+  char *tz;
 
   struct tm tm;
 
-  /* Warning: mktime is in local time so we need to calculate 
-   * offset to get UTC. C time handling is quirky */
-  t1 = 0;
-  tm = *gmtime(&t1);
-  t2 = mktime(&tm);
-  /* Calculate difference between UTC and local time. */
-  toff = (PLFLT) difftime(t1,t2);
-
+  /* Calculate seconds since the Unix epoch for 2005-12-01 UTC. */
+#if defined(WIN32)
+  /* Adopt the known result for POSIX-compliant systems. */
+  tstart = (PLFLT) 1133395200;
+#else
   tm.tm_year = 105; /* Years since 1900 = 2005 */
   tm.tm_mon = 11;   /* 0 == January, 11 = December */
   tm.tm_mday = 1;   /* 1 = 1st of month */
@@ -179,19 +176,24 @@
   tm.tm_min = 0;
   tm.tm_sec = 0;
 
+  /* Use POSIX-compliant equivalent of timegm GNU extension. */
+  tz = getenv("TZ");
+  setenv("TZ", "", 1);
+  tzset();
   /* tstart is a time_t value (cast to PLFLT) which represents the number
    * of seconds elapsed since 00:00:00 on January 1, 1970, Coordinated 
-   * Universal Time (UTC).  The actual value corresponds to 2005-12-01 in
-   * _local time_.  toff (calculated above and applied below) transforms that
-   * to a time_t value (cast to a PLFLT) corresponding to 2005-12-01 UTC.
-   * Aside from casting, the cross-platform result for tstart + toff should
-   * be identical to the result from the Linux timegm function (the inverse
-   * of the POSIX gmtime) for 2005-12-01. */
+   * Universal Time (UTC) on  2005-12-01 (UTC). */
   tstart = (PLFLT) mktime(&tm);
-
+  if (tz)
+    setenv("TZ", tz, 1);
+  else
+    unsetenv("TZ");
+  tzset();
+#endif
+   
   npts = 62;
 
-  xmin = tstart + toff;
+  xmin = tstart;
   xmax = xmin + npts*60.0*60.0*24.0;
   ymin = 0.0;
   ymax = 5.0;

Modified: trunk/examples/c++/x29.cc
===================================================================
--- trunk/examples/c++/x29.cc	2008-07-18 17:24:42 UTC (rev 8529)
+++ trunk/examples/c++/x29.cc	2008-07-18 17:40:06 UTC (rev 8530)
@@ -172,19 +172,16 @@
 {
   int i, npts;
   PLFLT xmin, xmax, ymin, ymax;
-  time_t t1, t2;
-  PLFLT tstart, toff;
+  PLFLT tstart;
+  char *tz;
 
   struct tm tm;
 
-  // Warning: mktime is in local time so we need to calculate 
-  // offset to get UTC. C time handling is quirky 
-  t1 = 0;
-  tm = *gmtime(&t1);
-  t2 = mktime(&tm);
-  // Calculate difference between UTC and local time.
-  toff = (PLFLT) difftime(t1,t2);
-
+  // Calculate seconds since the Unix epoch for 2005-12-01 UTC.
+#if defined(WIN32)
+  // Adopt the known result for POSIX-compliant systems.
+  tstart = (PLFLT) 1133395200;
+#else
   tm.tm_year = 105; // Years since 1900 = 2005
   tm.tm_mon = 11;   // 0 == January, 11 = December 
   tm.tm_mday = 1;   // 1 = 1st of month 
@@ -192,19 +189,24 @@
   tm.tm_min = 0;
   tm.tm_sec = 0;
 
-// tstart is a time_t value (cast to PLFLT) which represents the number
-// of seconds elapsed since 00:00:00 on January 1, 1970, Coordinated 
-// Universal Time (UTC).  The actual value corresponds to 2005-12-01 in
-// _local time_.  toff (calculated above and applied below) transforms that
-// to a time_t value (cast to a PLFLT) corresponding to 2005-12-01 UTC.
-// Aside from casting, the cross-platform result for tstart + toff should
-// be identical to the result from the Linux timegm function (the inverse
-// of the POSIX gmtime) for 2005-12-01.
+  // Use POSIX-compliant equivalent of timegm GNU extension.
+  tz = getenv("TZ");
+  setenv("TZ", "", 1);
+  tzset();
+  // tstart is a time_t value (cast to PLFLT) which represents the number
+  // of seconds elapsed since 00:00:00 on January 1, 1970, Coordinated 
+  // Universal Time (UTC) on  2005-12-01 (UTC).
   tstart = (PLFLT) mktime(&tm);
+  if (tz)
+    setenv("TZ", tz, 1);
+  else
+    unsetenv("TZ");
+  tzset();
+#endif
 
   npts = 62;
 
-  xmin = tstart + toff;
+  xmin = tstart;
   xmax = xmin + npts*60.0*60.0*24.0;
   ymin = 0.0;
   ymax = 5.0;


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