Floating point exception in TCL script

问题

i am using ns2 simulator and tcl script.on executing the following code it has raised floating point exception error. before i have changed the rate values in the following section of the code

$ns duplex-link $n0 $n2 2.0Mb 10ms RED
$ns duplex-link $n1 $n2 2.0Mb 10ms DropTail
$ns duplex-link $n2 $n3 1.1Mb 20ms DropTail
$ns duplex-link $n3 $n2 1.2Mb 10ms DropTail

it was working correctly but after it has been changed to the following i.e after i have used variables rate02,rate12,rate23,rate32 instead of the values floating point exception occurred. can any one help?

the whole tcl code is as follows:

    #Create a simulator object

    set ns [new Simulator]

    global set rate02 2.0Mb 
    global set rate12 2.0Mb
    global set rate23 1.1Mb
    global set rate32 1.2Mb

    #Define different colors for data flows (for NAM)
    $ns color 1 Blue
    $ns color 2 Red
    $ns color 3 Green

    #Open the NAM trace file
    set nf [open out.nam w]
    $ns namtrace-all $nf

    #Define a 'finish' procedure
    proc finish {} {
        global ns nf
        $ns flush-trace
        #Close the NAM trace file
        close $nf
        #Execute NAM on the trace file
        exec nam out.nam &
        exit 0
    }

    #Create four nodes
    set n0 [$ns node]
    set n1 [$ns node]
    set n2 [$ns node]
    set n3 [$ns node]

    #Create links between the nodes
    $ns duplex-link $n0 $n2 rate02 10ms RED
    $ns duplex-link $n1 $n2 rate12 10ms DropTail
    $ns duplex-link $n2 $n3 rate23 20ms DropTail
    $ns duplex-link $n3 $n2 rate32 10ms DropTail

        #Set Queue Size of link (n2-n3) to 10
        $ns queue-limit $n2 $n3 20
        $ns queue-limit $n3 $n2 22

        #Give node position (for NAM)
        $ns duplex-link-op $n0 $n2 orient right-down
        $ns duplex-link-op $n1 $n2 orient right-up
        $ns duplex-link-op $n2 $n3 orient right

        #Monitor the queue for link (n2-n3). (for NAM)
        $ns duplex-link-op $n2 $n3 queuePos 0.5


        #Setup a TCP connection
        set tcp1 [new Agent/TCP]
        $tcp1 set class_ 2
        $ns attach-agent $n0 $tcp1
        set sink [new Agent/TCPSink]
        $ns attach-agent $n3 $sink
        $ns connect $tcp1 $sink
        $tcp1 set fid_ 1
        #########################################
        #Setup a TCP connection
        set tcp3 [new Agent/TCP]
        $tcp3 set class_ 2
        $ns attach-agent $n3 $tcp3
        set sink2 [new Agent/TCPSink]
        $ns attach-agent $n2 $sink2
        $ns connect $tcp3 $sink2
        $tcp3 set fid_ 3

        #Setup a FTP over TCP connection
        set ftp3 [new Application/FTP]
        $ftp3 attach-agent $tcp3
        $ftp3 set type_ FTP
        ############################################
        #Setup a FTP over TCP connection
        set ftp1 [new Application/FTP]
        $ftp1 attach-agent $tcp1
        $ftp1 set type_ FTP

        #Setup a TCP connection
        set tcp2 [new Agent/TCP]
        $tcp2 set class_ 2
        $ns attach-agent $n1 $tcp2
        set sink [new Agent/TCPSink]
        $ns attach-agent $n3 $sink
        $ns connect $tcp2 $sink
        $tcp2 set fid_ 2

        #Setup a FTP over TCP connection
        set ftp2 [new Application/FTP]
        $ftp2 attach-agent $tcp2
        $ftp2 set type_ FTP

         proc openTrace { stopTime testName } {
            $self instvar ns_
            exec rm -f out.tr temp.rands
            set traceFile [open out.tr w]
            puts $traceFile "v testName $testName"
            $ns_ at $stopTime \
                "close $traceFile ; $self finish $testName"
            return $traceFile
        }
        proc traceQueues { node traceFile } {
            $self instvar ns_
            foreach nbr [$node neighbors] {
                $ns_ trace-queue $node $nbr $traceFile
                [$ns_ link $node $nbr] trace-dynamics $ns_ $traceFile
            }
        }


        #Schedule events for the CBR and FTP agents
        $ns at 0.1 "$ftp2 start"
        $ns at 1.0 "$ftp1 start"
        $ns at 1.0 "$ftp3 start"
        $ns at 4.0 "$ftp2 stop"
        $ns at 4.5 "$ftp1 stop"
        $ns at 4.5 "$ftp3 stop"

        #Detach tcp and sink agents (not really necessary)
        $ns at 4.5 "$ns detach-agent $n0 $tcp1 ; $ns detach-agent $n3 $sink"
        $ns at 4.5 "$ns detach-agent $n1 $tcp2 ; $ns detach-agent $n3 $sink"

        #Call the finish procedure after 5 seconds of simulation time
        $ns at 5.0 "finish"
        $ns run

回答1:

Unless that "NS2" thing redefines the Tcl's global command, the script should supposedly read something like this:

#Create a simulator object

set ns [new Simulator]

set rate02 2.0Mb 
set rate12 2.0Mb
set rate23 1.1Mb
set rate32 1.2Mb

# ...

#Create links between the nodes
$ns duplex-link $n0 $n2 $rate02 10ms RED
$ns duplex-link $n1 $n2 $rate12 10ms DropTail
$ns duplex-link $n2 $n3 $rate23 20ms DropTail
$ns duplex-link $n3 $n2 $rate32 10ms DropTail

# ...

In other words, there are two problems with your code:

The Tcl's global command has the semantics defined as global varname ?varname ...?, that is, it just declares the names which are passed to it as referring to global variables. Hence a call global set rate02 2.0Mb just declares the names "set", "rate02" and "2.0Mb" to denote global variables. Most probably not what you wanted.
the duplex-link subcommand probably expects a value as its "rate" argument, and you're passing it the name of a variable. Seemingly, some NS2 code then attempts to interpret such a string as a floating-point value, which fails for obvious reasons. Hence you have to dereference a variable to get its value when you want to pass that variable's value to a command. This is done using the set varname command or the shorthand notation using the $ syntax: $varname (more info about this).

Look like you should start with the Tcl tutorial which deals with these basics.

来源：https://stackoverflow.com/questions/11140086/floating-point-exception-in-tcl-script

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tcl