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Array elements inside proc

Posted by Arshad (Arshad), 3 January 2008
I am able to add an element to the array using the reference addr but I cannot print it or copy it to any other variable. This seems to be a bit surprising !!

proc foo {in} {
   upvar in addr
   puts $addr(3)
}

for {set count 1} {$count <= 4} {incr count} {
   set sa($count) $count
}
foo sa;


Error-
can't read "addr(3)": no such variable
parray sa;

Posted by admin (Graham Ellis), 3 January 2008
In Tcl, you must use a dollar sign if you want to refer to the contents of a variable, but you do not use a dollar sign if you are setting the value, or doing both at in the same context.

So you probably meant

upvar $in addr

and not

upvar in addr

since in the the name of the array that is passed in to the proc and is only used (and not set) within the upvar command, even if the array who's name it refers to may be set.

When I'm running a Tcl course, I always find myself spending longer on upvar than any other command.   And judging by the number of questions on it that I get here from people I have not trained, I think it's one of those things a lot of people need help with!



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