TCL脚本中的浮点异常 [英] Floating point exception in TCL script

问题描述

我正在使用 ns2 模拟器和 tcl 脚本.在执行以下代码时，它引发了浮点异常错误.在我更改以下代码部分中的速率值之前

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 

它工作正常，但在更改为以下内容后，即在我使用变量 rate02,rate12,rate23,rate32 而不是值之后发生了浮点异常.有人可以帮忙吗?

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?

整个tcl代码如下:

    #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

推荐答案

除非NS2"这个东西重新定义了 Tcl 的 global 命令，脚本应该是这样的:

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

# ...

换句话说，你的代码有两个问题:

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

• Tcl 的global 命令的语义定义为global varname ?varname ...?，也就是说，它只是声明names 传递给它作为引用全局变量.因此调用 global set rate02 2.0Mb 只声明名称set"、rate02"和2.0Mb"来表示全局变量.很可能不是您想要的.
• duplex-link 子命令可能需要一个值作为它的rate"参数，而你要传递给它一个变量的名称.em> 看起来，一些 NS2 代码然后试图将这样的字符串解释为浮点值，但由于明显的原因而失败.因此，当您想将该变量的值传递给命令时，您必须取消引用该变量以获取其值.这是使用 set varname 命令或使用 $ 语法的速记符号完成的:$varname (更多信息.

• 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).

看起来您应该从Tcl 教程开始处理这些基础知识.

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

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