TCL - More Array Commands - Iterating and use in procedures

Often you will want to loop through the contents of an associative array - without having to specify the elements explicitly. For this the array names and array get commands are very useful. With both you can give a (glob-style) pattern to select what elements you need:

foreach name [array names mydata] {

    puts "Data on \"$name\": $mydata($name)"
}

#
# Get names and values directly
#

 {
    puts "Data on \"$name\": $value"
}
foreach {name value} [array get mydata

]

Note, however, that the elements will not be returned in any predictable order: this has to do with the underlying "hash table". If you want a particular ordering (alphabetical for instance), use code like:

foreach name [lsort [array names mydata]] {

    puts "Data on \"$name\": $mydata($name)"

}

While arrays are great as a storage facility for some purposes, they are a bit tricky when you pass them to a procedure: they are actually collections of variables. This will not work:

proc print12 {a} {

   puts "$a(1), $a(2)"
}

set array(1) "A"

int12 $array

set array(2) "B"

p

r

The reason is very simple: an array does not have a value. Instead the above code should be:

proc print12 {array} {
   upvar $array a

(2)"
}

set array(1) "
puts "$a(1), $
aA"
set array(2) "B"



print12 array

So, instead of passing a "value" for the array, you pass the name. This gets aliased (via the upvar command) to a local variable (that behaves the as original array). You can make changes to the original array in this way too.

---

Example

#

# The example of the previous lesson revisited - to get a
# more general "database"
#


{
    upvar $db name

    # Cr
proc addname {db first last}

 eate a new ID (stored in the name array too for easy access)
incr name(ID)
    set id $name(ID)


ndex is simply a string!
    set name($id,last)  $last    ;# So w
set name($id,first) $first   ;# The 
ie can use both fixed and
                                 ;# varying parts
}

proc report {db} {

 [array names name
upvar $db name

    # Loop over the last names: make a map from last name to ID

    foreach 
n "*,last"] {
        #
        # Split the name to get the ID - the first part of the name!
        #

ap of last name to ID)
      
regexp {^[^,]+} $n id

        #
        # Store in a temporary array:
        # an "inverse" 
m  #
        set last       $name($n)
        set tmp($last) $id
    }

    #

h last [lsort [array names tmp]] {
        set id $tmp($last)
# Now we can easily print the names in the order we want!
    #
    forea
c
        puts "   $name($id,first) $name($id,last)"
    }
}

#
# Initialise the array and add a few names
#
set fictional_name(ID) 0


addname historical_name 
set historical_name(ID) 0

addname fictional_name Mary Poppins
addname fictional_name Uriah Heep
addname fictional_name Frodo Baggins
Rene Descartes

ame Julius Caesar

#
# Some simple report
addname historical_name Richard Lionheart
addname historical_name Leonardo "da Vinci"
addname historical_name Charles Baudelaire
addname historical_
ning
#
puts "Fictional characters:"
report fictional_name
puts "Historical characters:"


report historical_name