3 files changed, 38 insertions, 4 deletions
diff --git a/libformat/libformat/format.cxx b/libformat/libformat/format.cxx
index de8a782..6450093 100644
--- a/libformat/libformat/format.cxx
+++ b/libformat/libformat/format.cxx
@@ -2,6 +2,7 @@
 
 #include <cctype>     // to{upper,lower}()
 #include <algorithm>  // transform()
+#include <stdexcept>
 
 using namespace std;
 
@@ -10,9 +11,13 @@ namespace format
   string
   format_hello (const string& g, const string& n, volume v)
   {
-    string r (g);
+    if (const char* w = (g.empty () ? "empty greeting" :
+                         n.empty () ? "empty name"     : nullptr))
+      throw invalid_argument (w);
 
-    transform (r.begin (), r.end (), r.begin (),
+    string h (g);
+
+    transform (h.begin (), h.end (), h.begin (),
                [v] (char c) -> char
                {
                  switch (v)
@@ -24,6 +29,6 @@ namespace format
                  return c;
                });
 
-    return r += ", " + n + '!';
+    return h += ", " + n + '!';
   }
 }
diff --git a/libformat/libformat/format.hxx b/libformat/libformat/format.hxx
index 3641b67..489f63c 100644
--- a/libformat/libformat/format.hxx
+++ b/libformat/libformat/format.hxx
@@ -9,5 +9,7 @@ namespace format
   enum class volume {quiet, normal, loud};
 
   LIBFORMAT_SYMEXPORT std::string
-  format_hello (const std::string& greeting, const std::string& name, volume);
+  format_hello (const std::string& greeting,
+                const std::string& name,
+                volume = volume::normal);
 }
diff --git a/libformat/tests/basics/driver.cxx b/libformat/tests/basics/driver.cxx
index 03faea7..dbc9358 100644
--- a/libformat/tests/basics/driver.cxx
+++ b/libformat/tests/basics/driver.cxx
@@ -1,4 +1,5 @@
 #include <cassert>
+#include <stdexcept>
 
 #include <libformat/version.hxx>
 #include <libformat/format.hxx>
@@ -8,7 +9,33 @@ using namespace format;
 
 int main ()
 {
+  // Basics.
+  //
   assert (format_hello ("Hello", "World", volume::quiet)  == "hello, World!");
   assert (format_hello ("Hello", "World", volume::normal) == "Hello, World!");
   assert (format_hello ("Hello", "World", volume::loud)   == "HELLO, World!");
+
+  // Empty greeting.
+  //
+  try
+  {
+    format_hello ("", "World");
+    assert (false);
+  }
+  catch (const invalid_argument& e)
+  {
+    assert (e.what () == string ("empty greeting"));
+  }
+
+  // Empty name.
+  //
+  try
+  {
+    format_hello ("Hello", "");
+    assert (false);
+  }
+  catch (const invalid_argument& e)
+  {
+    assert (e.what () == string ("empty name"));
+  }
 }