Add basic support for Solaris.

include/spdlog/common.h

@@ -42,6 +42,8 @@
 #ifndef SPDLOG_ENABLE_SYSLOG
 #if defined (__linux__) || defined(__APPLE__)  || defined(__FreeBSD__)
 #define SPDLOG_ENABLE_SYSLOG
+#elif defined(sun) || defined(__sun)
+#define SPDLOG_ENABLE_SYSLOG
 #endif
 #endif
 

include/spdlog/details/os.h

@@ -250,7 +250,42 @@ inline int utc_minutes_offset(const std::tm& tm = details::os::localtime())
         offset -= tzinfo.StandardBias;
     return offset;
 #else
-    return static_cast<int>(tm.tm_gmtoff / 60);
+    long int offset_seconds;
+
+#if defined(sun) || defined(__sun)
+    // 'tm_gmtoff' field is BSD extension and it's missing on SunOS/Solaris
+    struct helper {
+        static long int calculate_gmt_offset(const std::tm & localtm = details::os::localtime(), const std::tm & gmtm = details::os::gmtime()) {
+            int local_year = localtm.tm_year + (1900 - 1);
+            int gmt_year = gmtm.tm_year + (1900 - 1);
+
+            long int days = (
+                // difference in day of year
+                localtm.tm_yday - gmtm.tm_yday
+
+                // + intervening leap days
+                + ((local_year >> 2) - (gmt_year >> 2))
+                - (local_year / 100 - gmt_year / 100)
+                + ((local_year / 100 >> 2) - (gmt_year / 100 >> 2))
+
+                // + difference in years * 365 */
+                + (long int)(local_year - gmt_year) * 365
+            );
+
+            long int hours = (24 * days) + (localtm.tm_hour - gmtm.tm_hour);
+            long int mins = (60 * hours) + (localtm.tm_min - gmtm.tm_min);
+            long int secs = (60 * mins) + (localtm.tm_sec - gmtm.tm_sec);
+
+            return secs;
+        }
+    };
+
+    offset_seconds = helper::calculate_gmt_offset(tm);
+#else
+    offset_seconds = tm.tm_gmtoff;
+#endif
+
+    return static_cast<int>(offset_seconds / 60);
 #endif
 }