Implement formatted output.

src/libqof/qof/gnc-datetime.cpp

@@ -102,7 +102,7 @@ public:
     operator struct tm() const;
     void now() { m_time = boost::local_time::local_sec_clock::local_time(tzp.get(boost::gregorian::day_clock::local_day().year())); }
     long offset() const;
-
+    std::string format(const char* format) const;
 private:
     LDT m_time;
 };
@@ -127,6 +127,18 @@ GncDateTimeImpl::offset() const
     return offset.total_seconds();
 }
 
+std::string
+GncDateTimeImpl::format(const char* format) const
+{
+    using Facet = boost::local_time::local_time_facet;
+    std::stringstream ss;
+    //The stream destructor frees the facet, so it must be heap-allocated.
+    auto output_facet(new Facet(format));
+    ss.imbue(std::locale(std::locale(), output_facet));
+    ss << m_time;
+    return ss.str();
+}
+
 /* =================== Presentation-class Implementations ====================*/
 GncDate::GncDate() : m_impl{new GncDateImpl} {}
 GncDate::GncDate(int year, int month, int day) :
@@ -167,3 +179,9 @@ GncDateTime::offset() const
 {
     return m_impl->offset();
 }
+
+std::string
+GncDateTime::format(const char* format) const
+{
+    return m_impl->format(format);
+}

src/libqof/qof/gnc-datetime.hpp

@@ -95,6 +95,7 @@ public:
     explicit operator struct tm() const;
     long offset() const;
     bool isnull (void) { return m_impl == nullptr; }
+    std::string format(const char* format) const;
 
 private:
     std::unique_ptr<GncDateTimeImpl> m_impl;

src/libqof/qof/test/gtest-gnc-datetime.cpp

@@ -69,3 +69,10 @@ TEST(gnc_datetime_constructors, test_struct_tm_constructor)
     EXPECT_EQ((24 + tm1.tm_hour - atime.offset() / 3600) % 24, tm.tm_hour);
     EXPECT_EQ(tm1.tm_min, tm.tm_min);
 }
+
+TEST(gnc_datetime_functions, test_format)
+{
+    GncDateTime atime(2394187200); //2045-11-13 12:00:00 Z
+    //Date only to finesse timezone issues. It will still fail in +12 DST.
+    EXPECT_EQ(atime.format("%d-%m-%Y"), "13-11-2045");
+}