20100905 NS2: Passing Values Between C++ and OTcl

NS2: Passing Values between C++ and OTcl domains by Teerawat Issariyakul http://www.ns2ultimate.com September 2010 http://www.ns2ultimate.com

Outline Introduction Motivation Executing OTcl statements C++  OTcl result(<constant string>) resultf(<string with printf format>) OTcl  C++: result() http://www.ns2ultimate.com

Introduction This is a series on how NS2 binds C++ and OTcl together. This is the second topic of the series: 1. Why Two Languages? 2. Binding C++ and OTcl classes 3. Variable binding 4. OTcl command: Invoking C++ statements from the OTcl domain 5. Eval and result: Invoking OTcl statements from the C++ domain 6. Object binding and object construction process. http://www.ns2ultimate.com

Motivation C++ is the place where users modify NS2 internal mechanism. Sometimes, we need to send/receive values between C++ and OTcl domain http://www.ns2ultimate.com MyObject C++ MyOTclObject OTcl Invoking OTcl function binding class name Constructor OTcl statement

Pre-requisite Pre-requisite Class binding [see here and here ] OTcl command [see here , here , and here] Given the bound environment Objective: 1. C++ variable delay_  Value in the OTcl domain 2. A Value in the OTcl domain  the C++ variable delay_ http://www.ns2ultimate.com C++: class = MyObject variable = delay_ OTcl: class = MyOTclObject variable = none

Executing OTcl Statement 1. Tcl::result(<constant string>); Pass <constant string> to the OTcl domain 2. Tcl::resultf(<string with printf format>); Use the <string with printf format> to create a string, and pass it to the OTcl domain. 3. Tcl::result() Receive a value from the OTcl domain. The return types is char* http://www.ns2ultimate.com

Environment Setup http://www.ns2ultimate.com Constructor OTcl command “ get-delay ” MyObject::MyObject(){ delay_ = 9.9; }; int MyObject::command(int argc, const char*const* argv) { if (argc==2) { if (strcmp(argv[1], “ get-delay ") == 0) { [ Passing delay_ to the OTcl ] return (TCL_OK); } } return TclObject::command(argc, argv); };

Environment Setup http://www.ns2ultimate.com OTcl file “result.tcl” set ns [new Simulator] set obj [new MyOTclObject] set d [$obj get-delay] puts "The variable d contains” puts "$d"

1. result(…): Details http://www.ns2ultimate.com Syntax Tcl::result(“<const string>”); where < const string > is a string you’d like to send to the OTcl domain. Note: In C++, we invoke function through an object Our example Tcl& tcl = Tcl::instance(); tcl.result(“A string from the C++ domain"); Create a Tcl object tcl Invoke function eval(…) throught tcl

1. result(…): Usage http://www.ns2ultimate.com Modify the OTcl command “ get-delay ” int MyObject::command(int argc, const char*const* argv) { Tcl& tcl = Tcl::instance(); if (argc==2) { if (strcmp(argv[1], “ get-delay ") == 0) { tcl.result("A string from the C++ domain"); return (TCL_OK); } } return TclObject::command(argc, argv); }; set ns [new Simulator] set obj [new MyOTclObject] set d [$obj get-delay] puts "The variable d contains” puts "$d" Run the Tcl simulation script “ result.tcl ” Output The string from the C++ domain is stored in the variable $d The value is displayed on this line

2. resultf(…): Details http://www.ns2ultimate.com Syntax (similar to evalf(…) ) Tcl::resultf(“<printf format>”,vars); where < printf format > is a formatting string. vars is the list of variables Note: In C++, we invoke function through an object Our example Tcl& tcl = Tcl::instance(); tcl.resultf("%2.2f\n", delay_); formatting string variable to be passed to the OTcl domain

2. resultf(…): Usage http://www.ns2ultimate.com Modify the OTcl command “ get-delay ” int MyObject::command(int argc, const char*const* argv) { Tcl& tcl = Tcl::instance(); if (argc==2) { if (strcmp(argv[1], “ get-delay ") == 0) { tcl.resultf("%2.2f\n", delay_); return (TCL_OK); } } return TclObject::command(argc, argv); }; set ns [new Simulator] set obj [new MyOTclObject] set d [$obj get-delay] puts "The variable d contains” puts "$d" Run the Tcl simulation script “ result.tcl ” Output The C++ variable delay_ was set to 9.9 in the constructor; It is now stored in the variable $d The value is displayed on this line

Environment Setup http://www.ns2ultimate.com Suppose we would like to initiate the C++ variable delay_ with an OTcl local variable $d The Tcl Simulation script “ result.tcl ” would be In C++, the constructor of class MyObject needs to Read the value of $d from the OTcl domain Stored the value in the variable delay_ set ns [new Simulator] set d 50 set obj [new MyOTclObject] puts "The variable d contains” puts "$d"

3. result(): Usage http://www.ns2ultimate.com Objective: Get a value returned from OTcl statement execution Syntax () Tcl::result(); Suppose we would like to initiate the C++ variable delay_ with an OTcl local variable $d Add the following code into the constructor Tcl& tcl = Tcl::instance(); tcl.eval("set d"); delay_ = atoi(tcl.result()); Execute “ set d ” in the OTcl domain; Get the value returned from the previous OTcl statement Note: set d returns the value stored in $d

3. result(): Usage http://www.ns2ultimate.com Modify the Constructor MyObject::MyObject() { Tcl& tcl = Tcl::instance(); tcl.eval("set d"); delay_ = atoi(tcl.result()); } set ns [new Simulator] set d 50 set obj [new MyOTclObject] puts "The variable d contains” puts "$d" Run the Tcl simulation script “ result.tcl ” Output When creating a MyOTclObject object, The C++ constructor of class MyObject is invoked. The value is displayed on this line Now, the value stored in delay_ is 50.

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

20100905 NS2: Passing Values Between C++ and OTcl

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20100905 NS2: Passing Values Between C++ and OTcl

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