Question

我使用的是Ns2和tcl脚本。在下面的代码中，我想使用全局变量rate12，它在表达式中的值为2Mb

 if { $queuesize>16 } {
     set RL [expr $Rc * $fdec * $hf]
    set rate12 [expr $rate12 * $RL]
    puts $rate12
 }

从proc记录中找到。但它显示以下错误：

ns: record _o104 file5: invalid bareword "Mb"
in expression "4_@_Mb * 0.40000000000000002";
should be "$Mb" or "{Mb}" or "Mb(...)" or ...
    (parsing expression "4Mb * 0.40000000000000...")
    invoked from within
"expr $rate12 * $RL"
    (procedure "record" line 26)
    invoked from within
"record _o104 file5"

我该如何修复错误？

整个代码是：

#Create a simulator object

set ns [new Simulator]

 global rate02 
 global rate12 
 global rate23 
 global rate32 

#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
# constants
global Rc 
global Fdec
global hf 

#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]

set rate02 2Mb
set rate12 4Mb
set rate23 2Mb
set rate32 0.1Mb

#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 16

#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

#creat file record infomation at queues

set queue03 [$ns monitor-queue $n2 $n3 [open qsize03.tr w] 0.05]
set qsize03 [open qsize03.tr w]


proc record {queue qsize} {
        global ns
        #set ns [Simulator instance]
        set time 0.1
        set now [$ns now]
        #print current qsize in $queuesize
        $queue instvar parrivals_ pdepartures_ bdros_ bdepartures_ pdrops_
        #set queuesize [expr $parrivals_ - $pdepartures_ - $pdrops_]
        set queuesize $parrivals_
        puts $queuesize
        puts $qsize "$now [expr $parrivals_ - $pdepartures_ - $pdrops_]"
        #puts "$now [expr $parrivals_ - $pdepartures_ - $pdrops_]"
        set $bdepartures_ 0

        set Rc 2
        set fdec 0.4
        set hf 0.5
        global rate12
        set n0 [$ns node]
        set n1 [$ns node]
        set n2 [$ns node]

        if { $queuesize>16 } {
        set RL [expr $Rc * $fdec * $hf]
        set rate12 [expr $rate12 * $RL]
        puts $rate12
        $ns duplex-link $n0 $n2 0.8Mb 10ms RED
        } elseif { $queuesize==20 } {
        puts "full"
        } else {
        puts "under"
        }

        $ns at [expr $now + $time] "record $queue $qsize"
}

#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 $n1 $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

#Schedule events for the CBR and FTP agents
$ns at 0.1 "$ftp2 start"
$ns at 0.5 "record $queue03 $qsize03"
$ns at 1.0 "$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

Answer 1

Tcl的expr命令不适用于具有类似Mb的单位的值。

因此它尝试解释值$rate12，即4Mb，但这不是有效的数字文字，因此您得到错误。结合您不支持表达的事实，例如你写道：

set rate12 [expr $rate12 * $RL]

而不是

set rate12 [expr {$rate12 * $RL}]

你得到expr的双重评估，这会产生误导性的错误信息（并且可能会慢很多）。

要解决此问题，您需要对没有单位的值进行计算，或者使用包含单位的小proc来执行此操作。

Answer 2

关键字global仅在proc的范围内有意义。要访问rate12，请在proc record的开头添加以下行：

global rate12

那应该解决你的问题。

更新

我的不好，我没有在proc中间看到global命令。问题是你刚开始的时候：

set rate12 4Mb

稍后，在proc record：

set rate12 [expr $rate12 * $RL]

根据Tcl，4Mb不是数字。我建议以下修复：

set rate12 4

或者，更具描述性：

set rateInMb12 4

如何在tcl表达式中使用全局字符串值

2 个答案:

更新