diff --git a/cmdopt.cpp b/cmdopt.cpp
index ec876652..a7f6a845 100644
--- a/cmdopt.cpp
+++ b/cmdopt.cpp
@@ -24,13 +24,17 @@
 using util::cmdopt::option::base;
 using util::cmdopt::option::bytes;
 using util::cmdopt::option::count;
+using util::cmdopt::option::null;
+using util::cmdopt::option::present;
 using util::cmdopt::option::value;
 using util::cmdopt::parser;
 
 
 ///////////////////////////////////////////////////////////////////////////////
 base::base (std::string _name):
-    m_name (_name)
+    m_name (_name),
+    m_required (false),
+    m_seen (false)
 { ; }
 
 
@@ -58,13 +62,18 @@ base::execute (const char *restrict)
 //-----------------------------------------------------------------------------
 void
 base::start (void)
-{ ; }
+{
+    m_seen = false;
+}
 
 
 //-----------------------------------------------------------------------------
 void
 base::finish (void)
-{ ; }
+{
+    if (m_required && !m_seen)
+        throw invalid_required (m_name);
+}
 
 
 //-----------------------------------------------------------------------------
@@ -75,6 +84,38 @@ base::name (void) const
 }
 
 
+//-----------------------------------------------------------------------------
+bool
+base::required (void) const
+{
+    return m_required;
+}
+
+
+//-----------------------------------------------------------------------------
+bool
+base::required (bool _required)
+{
+    return m_required = _required;
+}
+
+
+//-----------------------------------------------------------------------------
+bool
+base::seen (void) const
+{
+    return m_seen;
+}
+
+
+//-----------------------------------------------------------------------------
+bool
+base::seen (bool _seen)
+{
+    return m_seen = _seen;
+}
+
+
 ///////////////////////////////////////////////////////////////////////////////
 namespace util { namespace cmdopt { namespace option {
     template class value<uint16_t>;
@@ -96,6 +137,7 @@ void
 count<T>::execute (void)
 {
     ++this->data ();
+    this->seen (true);
 }
 
 
@@ -112,6 +154,9 @@ parser::scan (int argc, char *const *argv)
     CHECK_GE (argc, 0);
     CHECK    (argv);
 
+    for (auto &j: m_options)
+        j->start ();
+
     // start iterating after our program's name
     int i = 1;
     while (i < argc) {
@@ -130,6 +175,9 @@ parser::scan (int argc, char *const *argv)
         i += inc;
     }
 
+    for (auto &j: m_options)
+        j->finish ();
+
     return i;
 }
 
diff --git a/cmdopt.hpp b/cmdopt.hpp
index 56e642ce..92818027 100644
--- a/cmdopt.hpp
+++ b/cmdopt.hpp
@@ -38,8 +38,16 @@ namespace util { namespace cmdopt {
 
             std::string name (void) const;
 
+            bool required (void) const;
+            bool required (bool);
+
+            bool seen (void) const;
+            bool seen (bool);
+
         private:
             std::string m_name;
+            bool m_required;
+            bool m_seen;
         };
 
 
@@ -71,7 +79,7 @@ namespace util { namespace cmdopt {
 
         class bytes : public value<size_t> {
         public:
-            bytes (std::string name);
+            using value<size_t>::value;
 
             using value<size_t>::execute;
             void execute (const char *restrict) override;
@@ -91,6 +99,9 @@ namespace util { namespace cmdopt {
     class invalid_null : public error
     { using error::error; };
 
+    class invalid_required : public error
+    { using error::error; };
+
 
     class parser {
     public:
diff --git a/cmdopt.ipp b/cmdopt.ipp
index d0489a2d..4ee5d2dd 100644
--- a/cmdopt.ipp
+++ b/cmdopt.ipp
@@ -48,6 +48,8 @@ namespace util { namespace cmdopt {
         } catch (...) {
             throw invalid_value (__func__);
         }
+
+        seen (true);
     }