Promote 'CharArrayNullTerm' to EclIO::PaddedOutputString

Space-padded vectors of N (usually 8) characters is the typical
representation of character data in ECLIPSE output files.  Support
this type natively in the ECLIPSE IO library.

tests/test_PaddedOutputString.cpp

@@ -0,0 +1,95 @@
+#define BOOST_TEST_MODULE Padded_Output_String
+
+#include <boost/test/unit_test.hpp>
+
+#include <opm/io/eclipse/PaddedOutputString.hpp>
+
+// Convenience alias.
+template <std::size_t N>
+using PadString = ::Opm::EclIO::PaddedOutputString<N>;
+
+// =====================================================================
+
+BOOST_AUTO_TEST_SUITE(PadString8)
+
+BOOST_AUTO_TEST_CASE (Basic_Operations)
+{
+    // Default Constructor
+    {
+        const auto s = PadString<8>{};
+
+        BOOST_CHECK_EQUAL(s.c_str(), std::string(8, ' '));
+    }
+
+    // Construct from Constant String
+    {
+        const auto s = PadString<8>{"Inj-1"};
+
+        BOOST_CHECK_EQUAL(s.c_str(), std::string{"Inj-1   "});
+    }
+
+    // Copy Construction
+    {
+        const auto s1 = PadString<8>{"Inj-1"};
+        const auto s2 = s1;
+
+        BOOST_CHECK_EQUAL(s2.c_str(), std::string{"Inj-1   "});
+    }
+
+    // Move Construction
+    {
+        auto s1 = PadString<8>{"Inj-1"};
+        const auto s2 = std::move(s1);
+
+        BOOST_CHECK_EQUAL(s2.c_str(), std::string{"Inj-1   "});
+    }
+
+    // Assignment Operator
+    {
+        const auto s1 = PadString<8>{"Inj-1"};
+        auto s2 = PadString<8>{"Prod-2"};
+
+        s2 = s1;
+        BOOST_CHECK_EQUAL(s2.c_str(), std::string{"Inj-1   "});
+    }
+
+    // Move Assignment Operator
+    {
+        auto s1 = PadString<8>{"Inj-1"};
+        auto s2 = PadString<8>{"Prod-2"};
+
+        s2 = std::move(s1);
+        BOOST_CHECK_EQUAL(s2.c_str(), std::string{"Inj-1   "});
+    }
+
+    // Assign std::string
+    {
+        auto s = PadString<8>{"@Hi Hoo@"};
+
+        s = "Prod-2";
+        BOOST_CHECK_EQUAL(s.c_str(), std::string{"Prod-2  "});
+    }
+}
+
+BOOST_AUTO_TEST_CASE (String_Shortening)
+{
+    // Construct from string of more than N characters
+    {
+        const auto s = PadString<10>{
+            "String too long"
+        };
+
+        BOOST_CHECK_EQUAL(s.c_str(), std::string{"String too"});
+    }
+
+    // Assign string of more than N characters
+    {
+        auto s = PadString<11>{};
+
+        s = "This string has too many characters";
+
+        BOOST_CHECK_EQUAL(s.c_str(), std::string{"This string"});
+    }
+}
+
+BOOST_AUTO_TEST_SUITE_END()