1) OTcl commands allow users to call C++ functions from OTcl by binding C++ classes and functions to OTcl objects and commands. 2) This document demonstrates how to create an OTcl command called "show-delay" that displays the value of a C++ variable when called. 3) Key steps include adding the C++ variable and command function, compiling the changes, creating an OTcl object, and invoking the command to display the variable value. Modifying the variable updates the output when the command is rerun.

1. NS2: OTcl Command – Getting Started by Teerawat Issariyakul http://www.ns2ultimate.com July 2010 http://www.ns2ultimate.com

2. Outline Introduction Motivation What we would like to do OTcl Command http://www.ns2ultimate.com

3. Introduction This is a series on how NS2 binds C++ and OTcl together. This is the second topic of the series: Why Two Languages? Binding C++ and OTcl classes Variable binding OTcl command: Invoking C++ statements from the OTcl domain Eval and result: Invoking OTcl statements from the C++ domain Object binding and object construction process. http://www.ns2ultimate.com

4. Motivation OTcl is the place where users do the programming Sometimes, users need to call C++ function http://www.ns2ultimate.com MyObject programmer C++ MyOTclObject OTcl binding function binding class name delay_ show_delay(){ show “delay_” on the screen } show-delay

5. What we would like to do http://www.ns2ultimate.com C++: class = MyObject (see above) variable = delay_ function: show_delay() OTcl: class = MyOTclObject (see above) variable = none OTcl command: show-delay Binding class name [see here and here ] MyObject C++ MyOTclObject OTcl binding function binding class name (see above) delay_ show_delay(){ show “delay_” on the screen } show-delay

6. OTcl Command: Introduction Can be invoked from the OTcl domain ( show-delay ) Is bound to an OTcl object ( object ) Execute C++ domain ( show_delay() ) http://www.ns2ultimate.com

7. OTcl Command: C++ files In the following, I will use files in the previous post: otcl.cc, otcl.h, otcl.tcl Add a C++ variable delay_ to class MyObject http://www.ns2ultimate.com class MyObject : public TclObject { public: MyObject(); virtual ~MyObject(){}; protected: int count_; double delay_; double speed_; double virtual_time_; int is_running_; int command(int argc, const char*const* argv); }; otcl.h

8. OTcl Command: C++ files In the following, I will use files in the previous post: otcl.cc, otcl.h, otcl.tcl Add a C++ variable delay_ to class MyObject Constructor: Set the initial value of delay_ to be 7.7 Do not bind the variable Next step to use OTcl command to show the value of the variable delay_ on the screen http://www.ns2ultimate.com MyObject::MyObject() { delay_ = 7.7; } otcl.cc

9. OTcl Command: Definition Define within C++ class (e.g. MyObject ) Define by function “ command(…) ” Example: Insert the following into the file otcl.cc Do not forget to add a C++ variable delay_ to class MyObject http://www.ns2ultimate.com int MyObject::command(int argc, const char*const* argv) { if (argc==2) { if (strcmp(argv[1], "show-delay") == 0) { printf("Delay is %g\n", delay_); return (TCL_OK); } } return TclObject::command(argc, argv); }; OTcl command name what this OTcl command do

10. Summary of Key Steps Use files otcl.cc and otcl.h in the previous post Add the details as stated earlier run “ make ” to incorporate C++ changes in to NS2 [see detail here ] Create file otcl.tcl for testing 4.1 Create an OTcl object object 4.2 Invoke the OTcl command “show-delay” associated with object 4.4 Change the C++ constructor: set delay_ to be 9.9 4.5 Repeat 4.2 and 4.3 http://www.ns2ultimate.com

11. OTcl Command: Invocation File otcl.tcl Run the file otcl.tcl http://www.ns2ultimate.com set ns [new Simulator] set obj [new MyOTclObject ] $obj show-delay

12. OTcl Command: Invocation Modify the constructor Run the file otcl.tcl again http://www.ns2ultimate.com MyObject::MyObject() { delay_ = 9.9; }

13. For more information about NS 2 Please see this book from Springer T. Issaraiyakul and E. Hossain, “Introduction to Network Simulator NS2”, Springer 2009 http://www.ns2ultimate.com