Updated copy constructor and added parser path to correctly print program name in help for subparsers

README.md

@@ -36,6 +36,7 @@
      *    [Default Arguments](#default-arguments)
      *    [Gathering Remaining Arguments](#gathering-remaining-arguments)
      *    [Parent Parsers](#parent-parsers)
+     *    [Subparsers](#subparsers)
 *    [Further Examples](#further-examples)
      *     [Construct a JSON object from a filename argument](#construct-a-json-object-from-a-filename-argument)
      *     [Positional Arguments with Compound Toggle Arguments](#positional-arguments-with-compound-toggle-arguments)
@@ -692,6 +693,10 @@ bar_parser.parse_args({ "./main", "--bar", "YYY" });           // bar = YYY
 
 Note You must fully initialize the parsers before passing them via ```.add_parents```. If you change the parent parsers after the child parser, those changes will not be reflected in the child.
 
+### Subparsers
+
+Many programs split up their functionality into a number of sub-commands, for example, the `git` program can invoke sub-commands like `git checkout`, `git add`, and `git commit`. Splitting up functionality this way can be a particularly good idea when a program performs several different functions which require different kinds of command-line arguments. `ArgumentParser` supports the creation of such sub-commands with the `add_subparser()` member function.
+
 ## Further Examples
 
 ### Construct a JSON object from a filename argument

include/argparse/argparse.hpp

@@ -924,7 +924,8 @@ public:
   explicit ArgumentParser(std::string program_name = {},
                           std::string version = "1.0",
                           default_arguments add_args = default_arguments::all)
-      : m_program_name(std::move(program_name)), m_version(std::move(version)) {
+      : m_program_name(std::move(program_name)), m_version(std::move(version)),
+      m_parser_path(m_program_name) {
     if ((add_args & default_arguments::help) == default_arguments::help) {
       add_argument("-h", "--help")
           .action([&](const auto & /*unused*/) {
@@ -957,7 +958,9 @@ public:
         m_description(other.m_description), m_epilog(other.m_epilog),
         m_is_parsed(other.m_is_parsed),
         m_positional_arguments(other.m_positional_arguments),
-        m_optional_arguments(other.m_optional_arguments) {
+        m_optional_arguments(other.m_optional_arguments),
+        m_parser_path(other.m_parser_path),
+        m_subparsers(other.m_subparsers) {
     for (auto it = std::begin(m_positional_arguments);
          it != std::end(m_positional_arguments); ++it) {
       index_argument(it);
@@ -966,6 +969,10 @@ public:
          it != std::end(m_optional_arguments); ++it) {
       index_argument(it);
     }
+    for (auto it = std::begin(m_subparsers);
+        it != std::end(m_subparsers); ++it) {
+      m_subparser_map.insert_or_assign(it->get().m_program_name, it);
+    }
   }
 
   ~ArgumentParser() = default;
@@ -1106,7 +1113,7 @@ public:
   friend auto operator<<(std::ostream &stream, const ArgumentParser &parser)
       -> std::ostream & {
     stream.setf(std::ios_base::left);
-    stream << "Usage: " << parser.m_program_name << " [options] ";
+    stream << "Usage: " << parser.m_parser_path << " [options] ";
     for (const auto &argument : parser.m_positional_arguments) {
       stream << argument.m_names.front() << " ";
     }
@@ -1184,7 +1191,7 @@ public:
   }
 
   void add_subparser(ArgumentParser &parser) {
-
+    parser.m_parser_path = m_program_name + " " + parser.m_program_name;
     auto it = m_subparsers.emplace(std::cend(m_subparsers), parser);
     m_subparser_map.insert_or_assign(parser.m_program_name, it);
   }
@@ -1286,6 +1293,7 @@ private:
   std::list<Argument> m_positional_arguments;
   std::list<Argument> m_optional_arguments;
   std::map<std::string_view, argument_it, std::less<>> m_argument_map;
+  std::string m_parser_path;
   std::list<std::reference_wrapper<ArgumentParser>> m_subparsers;
   std::map<std::string_view, argument_parser_it, std::less<>> m_subparser_map;
 };