TCL — referencing "variable" variables

[Todd Lundstedt]

I am try to reference a variable variable name.. that is, the varName is not always the same, but it needs to be referenced by $varName.  Specifically, array names.

So for the following code, I have a varName set of “threadList”, and it is a list equal to “thread1 thread2 thread3”

I have two arrays defined, each one has 5 identically named elements.  The array names are thread1, and thread3

tcl> array names thread1

recBSnd recNSnd recTime recBRec recNRec recSite

tcl> array names thread3

recBSnd recNSnd recTime recBRec recNRec recSite

tcl> puts $threadList

thread1 thread2 thread3

Code:

foreach thrd $threadList {
 if {[info exists $thrd]} {
   append $sep $thrd(recBSnd) $sep $thrd(recBRec)
 }
}

My problem is arrays have to be referenced via the array name.  The array name (for the first run through) is “thread1”.

puts $thread1(recBSnd)

returns a value.  But I don’t know how to reference the array name by using a variable name.

Any help would be appreciated.

Thanks

Todd

Topic

[Jim Kosloskey]

Todd,

Have you tried subst?

Such as (assuming recBsnd has a value of 1)

echo [array get [subst $thrd] recBsnd]

which will return the key and value (as a list) – recBsnd 1

or if you just want the value:

echo [lindex [array get [subst $thrd] recBsnd

which will return 1 from the get list

Jim Kosloskey

email: jim.kosloskey@jim-kosloskey.com 29+ years Cloverleaf, 59 years IT - old fart.

[Todd Lundstedt]

Thanks Jim,

I should have thought of the subst command.  It’s been a while since I have done TCL coding from scratch.

Thanks again.

Todd

[Dick Bly]

dont forget cmds like  set and eval to perform functions on accessing variables for example you know that set x [set y] would be the equiv of set x $y but you can also do  set z 20;set y z ; set x [set $y]. now x has the vaue of 20.

eval comes in handy when you need to do things like

set x ${$name}(z)

for example

tcl>set ary(x) 3

tcl>set y ary

tcl>echo ${$y}(x) ;# attempt to use $y as an array name

Error: can’t read “$y”: no such varibale

tcl>

tcl>echo $[set y](x) an attemt to echo the value

$ary(x)

an eval completes the reference

tcl>eval echo $[set y](x)

3

tcl>

and then you could do

tcl>echo $$y(x)

Error: can’t read “y(x)”: variable isn’t array

tcl>echo $${y}(x)

$ary(x)

which then leads to

tcl>eval echo $${y}(x)

3

[Author]

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