Add GncDateTime::timestamp().

To provide a C++ implementation of gnc_date_timestamp and to avoid
using the expensive and localized GncDateTime::format().

libgnucash/engine/gnc-date.cpp

@@ -1075,7 +1075,7 @@ qof_strftime(gchar *buf, gsize max, const gchar *format, const struct tm *tm)
 gchar *
 gnc_date_timestamp (void)
 {
-    return gnc_print_time64(gnc_time(nullptr), "%Y%m%d%H%M%S");
+    return g_strdup(GncDateTime::timestamp().c_str());
 }
 
 /********************************************************************\

libgnucash/engine/gnc-datetime.cpp

@@ -236,6 +236,7 @@ public:
     std::string format(const char* format) const;
     std::string format_zulu(const char* format) const;
     std::string format_iso8601() const;
+    static std::string timestamp();
 private:
     LDT m_time;
     static const TD time_of_day[3];
@@ -466,6 +467,14 @@ GncDateTimeImpl::format_iso8601() const
     return str.substr(0, 19);
 }
 
+std::string
+GncDateTimeImpl::timestamp()
+{
+    GncDateTimeImpl gdt;
+    auto str = boost::posix_time::to_iso_string(gdt.m_time.local_time());
+    return str.substr(0, 8) + str.substr(9, 15);
+}
+
 /* Member function definitions for GncDateImpl.
  */
 GncDateImpl::GncDateImpl(const std::string str, const std::string fmt) :
@@ -600,6 +609,12 @@ GncDateTime::format_iso8601() const
     return m_impl->format_iso8601();
 }
 
+std::string
+GncDateTime::timestamp()
+{
+    return GncDateTimeImpl::timestamp();
+}
+
 /* GncDate */
 GncDate::GncDate() : m_impl{new GncDateImpl} {}
 GncDate::GncDate(int year, int month, int day) :

libgnucash/engine/gnc-datetime.hpp

@@ -152,7 +152,11 @@ public:
  *  @return a std::string in the format YYYY-MM-DD HH:MM:SS.
  */
     std::string format_iso8601() const;
-
+/** Get an undelimited string representing the current date and time.
+ *  @return a std::string in the format YYYYMMDDHHMMSS.
+ */
+    static std::string timestamp();
+    
 private:
     std::unique_ptr<GncDateTimeImpl> m_impl;
 };