command-line.h

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/*
 * Copyright (c) 2008 INRIA
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Authors: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
 */
#ifndef COMMAND_LINE_H
#define COMMAND_LINE_H
 
#include "callback.h"
#include "nstime.h"
#include "type-id.h"
 
#include <memory> // shared_ptr
#include <sstream>
#include <string>
#include <tuple>
#include <vector>
 
/**
 * @file
 * @ingroup commandline
 * ns3::CommandLine declaration.
 */
 
namespace ns3
{
 
/**
 * @ingroup core
 * @defgroup commandline Command Line Parsing
 *
 * A uniform way to specify program documentation,
 * allowed command line arguments and help strings,
 * and set any attribute or global value, all from
 * the command line directly.
 *
 * The main entry point is CommandLine
 */
 
/**
 * @ingroup commandline
 * @brief Parse command-line arguments
 *
 * Instances of this class can be used to parse command-line
 * arguments.  Programs can register a general usage message with
 * CommandLine::Usage, and arguments with CommandLine::AddValue.
 * Argument variable types with input streamers (`operator>>`)
 * can be set directly; more complex argument parsing
 * can be accomplished by providing a Callback.
 *
 * CommandLine also provides handlers for these standard arguments:
 * @verbatim
   --PrintGlobals:              Print the list of globals.
   --PrintGroups:               Print the list of groups.
   --PrintGroup=[group]:        Print all TypeIds of group.
   --PrintTypeIds:              Print all TypeIds.
   --PrintAttributes=[typeid]:  Print all attributes of typeid.
   --PrintVersion:              Print the ns-3 version.
   --PrintHelp:                 Print this help message. \endverbatim
 *
 * The more common \c \--version is a synonym for \c \--PrintVersion.
 *
 * The more common \c \--help is a synonym for \c \--PrintHelp; an example
 * is given below.
 *
 * CommandLine can also handle non-option arguments
 * (often called simply "positional" parameters: arguments which don't begin
 * with "-" or "--").  These can be parsed directly in to variables,
 * by registering arguments with AddNonOption in the order expected.
 * Additional non-option arguments encountered will be captured as strings.
 *
 * Finally, CommandLine processes Attribute and GlobalValue arguments.
 * Default values for specific attributes can be set using a shorthand
 * argument name.
 *
 * In use, arguments are given in the form
 * @verbatim
   --arg=value --toggle first-non-option\endverbatim
 * Most arguments expect a value, as in the first form, \c \--arg=value.
 * Toggles, corresponding to boolean arguments, can be given in any of
 * the forms
 * @verbatim
   --toggle1 --toggle2=1 --toggle3=t --toggle4=true \endverbatim
 * The first form changes the state of toggle1 from its default;
 * all the rest set the corresponding boolean variable to true.
 * \c 0, \c f and \c false are accepted to set the variable to false.
 * Option arguments can appear in any order on the command line,
 * even intermixed with non-option arguments.
 * The order of non-option arguments is preserved.
 *
 * Option arguments can be repeated on the command line; the last value given
 * will be the final value used.  For example,
 * @verbatim
   --arg=one --toggle=f --arg=another --toggle \endverbatim
 * The variable set by \c \--arg will end up with the value \c "another";
 * the boolean set by \c \--toggle will end up as \c true.
 *
 * Because arguments can be repeated it can be hard to decipher what
 * value each variable ended up with, especially when using boolean toggles.
 * Suggested best practice is for scripts to report the values of all items
 * settable through CommandLine, as done by the example below.
 *
 *
 * CommandLine can set the initial value of every attribute in the system
 * with the \c \--TypeIdName::AttributeName=value syntax, for example
 * @verbatim
   --Application::StartTime=3s \endverbatim
 * In some cases you may want to highlight the use of a particular
 * attribute for a simulation script.  For example, you might want
 * to make it easy to set the \c Application::StartTime using
 * the argument \c \--start, and have its help string show as part
 * of the help message.  This can be done using the
 * @link AddValue(const std::string&, const std::string&) AddValue (name, attributePath) \endlink
 * method.
 *
 * CommandLine can also set the value of every GlobalValue
 * in the system with the \c \--GlobalValueName=value syntax, for example
 * @verbatim
   --SchedulerType=HeapScheduler \endverbatim
 *
 * A simple example of CommandLine is in `src/core/example/command-line-example.cc`
 * See that file for an example of handling non-option arguments.
 *
 * The heart of that example is this code:
 *
 * @code
 *    int         intArg  = 1;
 *    bool        boolArg = false;
 *    std::string strArg  = "strArg default";
 *
 *    CommandLine cmd (__FILE__);
 *    cmd.Usage ("CommandLine example program.\n"
 *               "\n"
 *               "This little program demonstrates how to use CommandLine.");
 *    cmd.AddValue ("intArg",  "an int argument",       intArg);
 *    cmd.AddValue ("boolArg", "a bool argument",       boolArg);
 *    cmd.AddValue ("strArg",  "a string argument",     strArg);
 *    cmd.AddValue ("anti",    "ns3::RandomVariableStream::Antithetic");
 *    cmd.AddValue ("cbArg",   "a string via callback", MakeCallback (SetCbArg));
 *    cmd.Parse (argc, argv);
 * @endcode
 * after which it prints the values of each variable.  (The \c SetCbArg function
 * is not shown here; see `src/core/example/command-line-example.cc`)
 *
 * Here is the output from a few runs of that program:
 *
 * @verbatim
   $ ./ns3 run "command-line-example"
   intArg:   1
   boolArg:  false
   strArg:   "strArg default"
   cbArg:    "cbArg default"
 
   $ ./ns3 run "command-line-example --intArg=2 --boolArg --strArg=Hello --cbArg=World"
   intArg:   2
   boolArg:  true
   strArg:   "Hello"
   cbArg:    "World"
 
   $ ./ns3 run "command-line-example --help"
   ns3-dev-command-line-example-debug [Program Arguments] [General Arguments]
 
   CommandLine example program.
 
   This little program demonstrates how to use CommandLine.
 
   Program Arguments:
       --intArg:   an int argument [1]
       --boolArg:  a bool argument [false]
       --strArg:   a string argument [strArg default]
       --anti:     Set this RNG stream to generate antithetic values
 (ns3::RandomVariableStream::Antithetic) [false]
       --cbArg:    a string via callback
 
   General Arguments:
       --PrintGlobals:              Print the list of globals.
       --PrintGroups:               Print the list of groups.
       --PrintGroup=[group]:        Print all TypeIds of group.
       --PrintTypeIds:              Print all TypeIds.
       --PrintAttributes=[typeid]:  Print all attributes of typeid.
       --PrintVersion:              Print the ns-3 version.
       --PrintHelp:                 Print this help message. \endverbatim
 *
 * Having parsed the arguments, some programs will need to perform
 * some additional validation of the received values.  A common issue at this
 * point is to discover that the supplied arguments are incomplete or
 * incompatible.  Suggested best practice is to supply an error message
 * and the complete usage message.  For example,
 *
 * @code
 *   int value1;
 *   int value2;
 *
 *   CommandLine cmd (__FILE__);
 *   cmd.Usage ("...");
 *   cmd.AddValue ("value1", "first value", value1);
 *   cmd.AddValue ("value2", "second value", value1);
 *
 *   cmd.Parse (argc, argv);
 *
 *   if (value1 * value2 < 0)
 *     {
 *       std::cerr << "value1 and value2 must have the same sign!" << std::endl;
 *       std::cerr << cmd;
 *       exit (-1);
 *     }
 * @endcode
 *
 * Finally, note that for examples which will be run by \c test.py
 * the preferred declaration of a CommandLine instance is
 *
 * @code
 *     CommandLine cmd (__FILE__);
 * @endcode
 * This will ensure that the program usage and arguments can be added to
 * the Doxygen documentation automatically.
 */
class CommandLine
{
  public:
    /** Constructor */
    CommandLine();
    /**
     * Construct and register the source file name.
     * This would typically be called by
     *     CommandLine cmd (__FILE__);
     *
     * This form is required to generate Doxygen documentation of the
     * arguments and options.
     *
     * @param [in] filename The source file name.
     */
    CommandLine(const std::string& filename);
    /**
     * Copy constructor
     *
     * @param [in] cmd The CommandLine to copy from
     */
    CommandLine(const CommandLine& cmd);
    /**
     * Assignment
     *
     * @param [in] cmd The CommandLine to assign from
     * @return The CommandLine
     */
    CommandLine& operator=(const CommandLine& cmd);
    /** Destructor */
    ~CommandLine();
 
    /**
     * Supply the program usage and documentation.
     *
     * @param [in] usage Program usage message to write with \c \--help.
     */
    void Usage(const std::string& usage);
 
    /**
     * Add a program argument, assigning to POD
     *
     * @param [in] name The name of the program-supplied argument
     * @param [in] help The help text used by \c \--PrintHelp
     * @param [out] value A reference to the variable where the
     *        value parsed will be stored (if no value
     *        is parsed, this variable is not modified).
     */
    template <typename T>
    void AddValue(const std::string& name, const std::string& help, T& value);
 
    /**
     * Retrieve the \c char* in \c char* and add it as a program argument
     *
     * This variant it used to receive C string pointers
     * from the python bindings.
     *
     * The C string result stored in \c value will be null-terminated,
     * and have a maximum length of \c (num - 1).
     * The result will be truncated to fit, if necessary.
     *
     * @param [in] name The name of the program-supplied argument
     * @param [in] help The help text used by \c \--PrintHelp
     * @param [out] value A pointer pointing to the beginning
     *        of a null-terminated C string buffer provided by
     *        the caller. The parsed value will be stored in
     *        that buffer (if no value is parsed, this
     *        variable is not modified).
     * @param num The size of the buffer pointed to by \c value,
     *        including any terminating null.
     */
    void AddValue(const std::string& name, const std::string& help, char* value, std::size_t num);
    /**
     * Callback function signature for
     * AddValue(const std::string&,const std::string&,Callback<bool,const std::string>).
     *
     * @param [in] value The argument value.
     */
    typedef bool (*Callback)(const std::string& value);
 
    /**
     * Add a program argument, using a Callback to parse the value
     *
     * @param [in] name The name of the program-supplied argument
     * @param [in] help The help text used by \c \--help
     * @param [in] callback A Callback function that will be invoked to parse and
     *   store the value.
     * @param [in] defaultValue Optional default value for argument.
     *
     * The callback should have the signature
     * CommandLine::Callback
     */
    void AddValue(const std::string& name,
                  const std::string& help,
                  ns3::Callback<bool, const std::string&> callback,
                  const std::string& defaultValue = "");
 
    /**
     * Add a program argument as a shorthand for an Attribute.
     *
     * @param [in] name The name of the program-supplied argument.
     * @param [out] attributePath The fully-qualified name of the Attribute
     */
    void AddValue(const std::string& name, const std::string& attributePath);
 
    /**
     * Add a non-option argument, assigning to POD
     *
     * @param [in] name The name of the program-supplied argument
     * @param [in] help The help text used by \c \--PrintHelp
     * @param [out] value A reference to the variable where the
     *        value parsed will be stored (if no value
     *        is parsed, this variable is not modified).
     */
    template <typename T>
    void AddNonOption(const std::string& name, const std::string& help, T& value);
 
    /**
     * Get extra non-option arguments by index.
     * This allows CommandLine to accept more non-option arguments than
     * have been configured explicitly with AddNonOption().
     *
     * This is only valid after calling Parse().
     *
     * @param [in] i The index of the non-option argument to return.
     * @return The i'th non-option argument, as a string.
     */
    std::string GetExtraNonOption(std::size_t i) const;
 
    /**
     * Get the total number of non-option arguments found,
     * including those configured with AddNonOption() and extra non-option
     * arguments.
     *
     * This is only valid after calling Parse().
     *
     * @returns the number of non-option arguments found.
     */
    std::size_t GetNExtraNonOptions() const;
 
    /**
     * Parse the program arguments
     *
     * @param [in] argc The 'argc' variable: number of arguments (including the
     *        main program name as first element).
     * @param [in] argv The 'argv' variable: a null-terminated array of strings,
     *        each of which identifies a command-line argument.
     *
     * Obviously, this method will parse the input command-line arguments and
     * will attempt to handle them all.
     *
     * As a side effect, this method saves the program basename, which
     * can be retrieved by GetName().
     */
    void Parse(int argc, char* argv[]);
 
    /**
     * Parse the program arguments.
     *
     * This version may be convenient when synthesizing arguments
     * programmatically.  Other than the type of argument this behaves
     * identically to Parse(int, char *)
     *
     * @param [in] args The vector of arguments.
     */
    void Parse(std::vector<std::string> args);
 
    /**
     * Get the program name
     *
     * @return The program name.  Only valid after calling Parse()
     */
    std::string GetName() const;
 
    /**
     * @brief Print program usage to the desired output stream
     *
     * Handler for \c \--PrintHelp and \c \--help:  print Usage(), argument names, and help strings
     *
     * Alternatively, an overloaded operator << can be used:
     * @code
     *       CommandLine cmd (__FILE__);
     *       cmd.Parse (argc, argv);
     *     ...
     *
     *       std::cerr << cmd;
     * @endcode
     *
     * @param [in,out] os The output stream to print on.
     */
    void PrintHelp(std::ostream& os) const;
 
    /**
     * Get the program version.
     *
     * @return The program version
     */
    std::string GetVersion() const;
 
    /**
     * Print ns-3 version to the desired output stream
     *
     * Handler for \c \--PrintVersion and \c \--version.
     *
     * @param [in,out] os The output stream to print on.
     */
    void PrintVersion(std::ostream& os) const;
 
  private:
    /**
     * @ingroup commandline
     * @brief The argument abstract base class
     */
    class Item
    {
      public:
        std::string m_name; /**< Argument label:  \c \--m_name=... */
        std::string m_help; /**< Argument help string */
        virtual ~Item();    /**< Destructor */
        /**
         * Parse from a string.
         *
         * @param [in] value The string representation
         * @return \c true if parsing the value succeeded
         */
        virtual bool Parse(const std::string& value) const = 0;
        /**
         * @return \c true if this item has a default value.
         */
        virtual bool HasDefault() const;
        /**
         * @return The default value
         */
        virtual std::string GetDefault() const = 0;
 
        // end of class Item
    };
 
    /**
     * @ingroup commandline
     * @brief An argument Item assigning to POD
     */
    template <typename T>
    class UserItem : public Item
    {
      public:
        // Inherited
        bool Parse(const std::string& value) const override;
        bool HasDefault() const override;
        std::string GetDefault() const override;
 
        T* m_valuePtr;         /**< Pointer to the POD location */
        std::string m_default; /**< String representation of default value */
 
        // end of class UserItem
    };
 
    /**
     * @ingroup commandline
     * @brief Extension of Item for extra non-options, stored as strings.
     */
    class StringItem : public Item
    {
      public:
        // Inherited
        bool Parse(const std::string& value) const override;
        bool HasDefault() const override;
        std::string GetDefault() const override;
 
        /**
         * The argument value.
         * @internal This has to be \c mutable because the Parse()
         * function is \c const in the base class Item.
         */
        mutable std::string m_value;
 
        // end of class StringItem
    };
 
    /**
     * @ingroup commandline
     * @brief Extension of Item for \c char*.
     */
    class CharStarItem : public Item
    {
      public:
        // Inherited
        bool Parse(const std::string& value) const override;
        bool HasDefault() const override;
        std::string GetDefault() const override;
 
        /** The buffer to write in to. */
        char* m_buffer;
        /** The size of the buffer, including terminating null. */
        std::size_t m_size;
        /** The default value. */
        std::string m_default;
 
        // end of class CharStarItem
    };
 
    /**
     * @ingroup commandline
     * @brief An argument Item using a Callback to parse the input
     */
    class CallbackItem : public Item
    {
      public:
        // Inherited
        bool Parse(const std::string& value) const override;
        bool HasDefault() const override;
        std::string GetDefault() const override;
 
        ns3::Callback<bool, const std::string&> m_callback; /**< The Callback */
        std::string m_default; /**< The default value, as a string, if it exists. */
 
        // end of class CallbackItem
    };
 
    /**
     * Tuple type returned by GetOptionName().
     *
     * | Field    | Meaning
     * |----------|--------------------------------------------
     * | `get<0>` | Is this an option (beginning with `-`)?
     * | `get<1>` | The option name (after any `-`, before `=`)
     * | `get<2>` | The value (after any `=`)
     */
    using HasOptionName = std::tuple<bool, std::string, std::string>;
 
    /**
     * Strip leading `--` or `-` from options.
     *
     * @param [in] param Option name to search
     * @returns \c false if none found, indicating this is a non-option.
     */
    HasOptionName GetOptionName(const std::string& param) const;
    /**
     * Handle hard-coded options.
     *
     * \note: if any hard-coded options are found this function exits.
     *
     * @param [in] args Vector of hard-coded options to handle.
     */
    void HandleHardOptions(const std::vector<std::string>& args) const;
 
    /**
     * Handle an option in the form \c param=value.
     *
     * @param [in] param The option string.
     * @returns \c true if this was really an option.
     */
    bool HandleOption(const std::string& param) const;
 
    /**
     * Handle a non-option
     *
     * @param [in] value The command line non-option value.
     * @return \c true if \c value could be parsed correctly.
     */
    bool HandleNonOption(const std::string& value);
 
    /**
     * Match name against the program or general arguments,
     * and dispatch to the appropriate handler.
     *
     * @param [in] name The argument name
     * @param [in] value The command line value
     * @returns \c true if the argument was handled successfully
     */
    bool HandleArgument(const std::string& name, const std::string& value) const;
    /**
     * Callback function to handle attributes.
     *
     * @param [in] name The full name of the Attribute.
     * @param [in] value The value to assign to \pname{name}.
     * @return \c true if the value was set successfully, false otherwise.
     */
    static bool HandleAttribute(const std::string& name, const std::string& value);
 
    /**
     * Handler for \c \--PrintGlobals:  print all global variables and values
     * @param [in,out] os The output stream to print on.
     */
    void PrintGlobals(std::ostream& os) const;
    /**
     * Handler for \c \--PrintAttributes:  print the attributes for a given type
     * as well as its parents.
     *
     * @param [in,out] os the output stream.
     * @param [in] type The type name whose Attributes should be displayed,
     */
    void PrintAttributes(std::ostream& os, const std::string& type) const;
    /**
     * Print the Attributes for a single type.
     *
     * @param [in,out] os the output stream.
     * @param [in] tid The TypeId whose Attributes should be displayed,
     * @param [in] header A header line to print if \c tid has Attributes
     */
    void PrintAttributeList(std::ostream& os, const TypeId tid, std::stringstream& header) const;
    /**
     * Handler for \c \--PrintGroup:  print all types belonging to a given group.
     *
     * @param [in,out] os The output stream.
     * @param [in] group The name of the TypeId group to display
     */
    void PrintGroup(std::ostream& os, const std::string& group) const;
    /**
     * Handler for \c \--PrintTypeIds:  print all TypeId names.
     *
     * @param [in,out] os The output stream.
     */
    void PrintTypeIds(std::ostream& os) const;
    /**
     * Handler for \c \--PrintGroups:  print all TypeId group names
     *
     * @param [in,out] os The output stream.
     */
    void PrintGroups(std::ostream& os) const;
    /**
     * Copy constructor implementation
     *
     * @param [in] cmd CommandLine to copy
     */
    void Copy(const CommandLine& cmd);
    /** Remove all arguments, Usage(), name */
    void Clear();
    /**
     * Append usage message in Doxygen format to the file indicated
     * by the NS_COMMANDLINE_INTROSPECTION environment variable.
     * This is typically only called once, by Parse().
     */
    void PrintDoxygenUsage() const;
 
    /** Argument list container */
    using Items = std::vector<std::shared_ptr<Item>>;
 
    /**
     * @brief Checks for duplicate item names in a list of items.
     *
     * This function checks for the existence of an item with the same name as the one provided in
     * the list of items. If a duplicate is found, an error message is generated and the program is
     * aborted.
     *
     * @param[in] name The name of the item to check.
     * @param[in] optType The type of option that the item represents (e.g. "option", "non-option").
     * @param[in] items A list of Items to check for duplicate names.
     */
    void CheckForDuplicateItemNameError(std::string name, std::string optType, const Items& items);
    /**
     * @brief Test for duplicate option arguments.
     *
     * @param name The name of the option argument to test for.
     */
    void TestForDuplicateOption(std::string name);
    /**
     * Tests for duplicate non-option arguments.
     *
     * @param name The name of the non-option argument to test for.
     */
    void TestForDuplicateNonOption(std::string name);
 
    /** The list of option arguments */
    Items m_options;
    /** The list of non-option arguments */
    Items m_nonOptions;
 
    /** The expected number of non-option arguments */
    std::size_t m_NNonOptions;
    /** The number of actual non-option arguments seen so far. */
    std::size_t m_nonOptionCount;
    /** The Usage string */
    std::string m_usage;
    /** The source file name (without `.cc`), as would be given to `ns3 run` */
    std::string m_shortName;
 
    // end of class CommandLine
};
 
/**
 * @ingroup commandline
 * @defgroup commandlinehelper Helpers to specialize UserItem
 */
/**
 * @ingroup commandlinehelper
 * @brief Helpers for CommandLine to specialize UserItem
 */
namespace CommandLineHelper
{
 
/**
 * @ingroup commandlinehelper
 * @brief Helpers to specialize CommandLine::UserItem::Parse()
 *
 * @param [in] value The argument name
 * @param [out] dest The argument location
 * @tparam T \deduced The type being specialized
 * @return \c true if parsing was successful
 */
template <typename T>
bool UserItemParse(const std::string& value, T& dest);
/**
 * @brief Specialization of CommandLine::UserItem::Parse() to \c bool
 *
 * @param [in] value The argument name
 * @param [out] dest The boolean variable to set
 * @return \c true if parsing was successful
 */
template <>
bool UserItemParse<bool>(const std::string& value, bool& dest);
/**
 * @brief Specialization of CommandLine::UserItem::Parse() to \c uint8_t
 * to distinguish from \c char
 *
 * @param [in] value The argument name
 * @param [out] dest The \c uint8_t variable to set
 * @return \c true if parsing was successful
 */
template <>
bool UserItemParse<uint8_t>(const std::string& value, uint8_t& dest);
 
/**
 * @ingroup commandlinehelper
 * @brief Helper to specialize CommandLine::UserItem::GetDefault() on types
 * needing special handling.
 *
 * @param [in] defaultValue The default value from the UserItem.
 * @return The string representation of value.
 * @{
 */
template <typename T>
std::string GetDefault(const std::string& defaultValue);
template <>
std::string GetDefault<bool>(const std::string& defaultValue);
template <>
std::string GetDefault<Time>(const std::string& defaultValue);
/**@}*/
 
} // namespace CommandLineHelper
 
} // namespace ns3
 
/********************************************************************
 *  Implementation of the templates declared above.
 ********************************************************************/
 
namespace ns3
{
 
template <typename T>
void
CommandLine::AddValue(const std::string& name, const std::string& help, T& value)
{
    TestForDuplicateOption(name);
    auto item = std::make_shared<UserItem<T>>();
    item->m_name = name;
    item->m_help = help;
    item->m_valuePtr = &value;
 
    std::stringstream ss;
    ss << value;
    item->m_default = ss.str(); // Including white spaces
 
    m_options.push_back(item);
}
 
template <typename T>
void
CommandLine::AddNonOption(const std::string& name, const std::string& help, T& value)
{
    TestForDuplicateNonOption(name);
    auto item = std::make_shared<UserItem<T>>();
    item->m_name = name;
    item->m_help = help;
    item->m_valuePtr = &value;
 
    std::stringstream ss;
    ss << value;
    ss >> item->m_default;
    m_nonOptions.push_back(item);
    ++m_NNonOptions;
}
 
template <typename T>
bool
CommandLine::UserItem<T>::HasDefault() const
{
    return !m_default.empty();
}
 
template <typename T>
std::string
CommandLine::UserItem<T>::GetDefault() const
{
    return CommandLineHelper::GetDefault<T>(m_default);
}
 
template <typename T>
std::string
CommandLineHelper::GetDefault(const std::string& defaultValue)
{
    return defaultValue;
}
 
template <typename T>
bool
CommandLine::UserItem<T>::Parse(const std::string& value) const
{
    return CommandLineHelper::UserItemParse<T>(value, *m_valuePtr);
}
 
template <typename T>
bool
CommandLineHelper::UserItemParse(const std::string& value, T& dest)
{
    std::istringstream iss;
    iss.str(value);
    iss >> dest;
    return !iss.bad() && !iss.fail();
}
 
/**
 * Overloaded operator << to print program usage
 * (shortcut for CommandLine::PrintHelper)
 *
 * @see CommandLine::PrintHelper
 *
 * Example usage:
 * @code
 *    CommandLine cmd (__FILE__);
 *    cmd.Parse (argc, argv);
 *    ...
 *
 *    std::cerr << cmd;
 * @endcode
 *
 * @param [in,out] os The stream to print on.
 * @param [in] cmd The CommandLine describing the program.
 * @returns The stream.
 */
std::ostream& operator<<(std::ostream& os, const CommandLine& cmd);
 
} // namespace ns3
 
#endif /* COMMAND_LINE_H */