add a function in the NeXus lib which gives the time in ISO8601.

src/external/nexus/PNeXus.cpp

@@ -73,6 +73,9 @@
 #include <stdexcept>
 #include <cstring>
 #include <cmath>
+#include <chrono>
+#include <ctime>
+#include <iomanip>
 
 #include "Minuit2/MnStrategy.h"
 #include "Minuit2/MnMinimize.h"
@@ -130,6 +133,29 @@ nxs::HDFType nxs::checkHDFType(const std::string& filename) {
   return nxs::HDFType::Unknown;
 }
 
+//=============================================================================
+// nxs::getIso8601TimestampLocal - current time stamp in ISO8601 format
+//=============================================================================
+std::string nxs::getIso8601TimestampLocal() {
+  auto now = std::chrono::system_clock::now();
+  std::time_t now_c = std::chrono::system_clock::to_time_t(now);
+  std::tm* local_tm = std::localtime(&now_c);
+
+  // Get timezone offset
+  char tz_offset[10];
+  std::strftime(tz_offset, sizeof(tz_offset), "%z", local_tm);
+
+  std::ostringstream oss;
+  oss << std::put_time(local_tm, "%Y-%m-%dT%H:%M:%S");
+
+  // Insert colon in timezone offset: +0100 → +01:00
+  std::string tz_str(tz_offset);
+  tz_str.insert(3, ":");
+  oss << tz_str;
+
+  return oss.str();
+}
+
 #ifdef HAVE_HDF4
 //=============================================================================
 // nxH4::PNeXusDeadTime Constructor

src/external/nexus/PNeXus.h

@@ -181,6 +181,14 @@ enum class HDFType {
  */
 HDFType checkHDFType(const std::string& filename);
 
+/**
+ * @brief get the current time and return it as na IOS8601
+ * time stamp.
+ *
+ * @return ISO 8601 time stamp string
+ */
+std::string getIso8601TimestampLocal();
+
 } // end namespace nxs
 
 #ifdef HAVE_HDF4
@@ -1089,7 +1097,7 @@ private:
   static int32 convertToHdf4Type(H4DataType dataType);
 };
 
-}
+} // end namespace nxH4
 #endif // HAVE_HDF4
 
 /**
@@ -2072,6 +2080,6 @@ private:
   void ReadDatasetAttributes(H5::DataSet& dataset, PNXdata<T>& data);
 };
 
-}
+} // end namespace nxH5
 
 #endif // _PNEXUS_H_