The man page for llength is http://purl.org/tcl/home/man/tcl8.4/TclCmd/llength.htm
This command returns the number of elements in the list. If the string is not a well-formed list, an error will be thrown.
caspian: Make sure to give llength the list, not just the name variable where the list is stored. For example:
# This is the right way to do it.
set mylist {a b c}
# LV writes: technically, _this_ is the right way to do it, at least
# for cases more complex than a simple a, b, and c...
# set mylist [list a b c]
llength $mylist
# This is the WRONG way to do it.
# This won't return an error, but it will always return "1",
# no matter how long or short your list is.
set mylist {a b c}
llength mylistThis is one of those places where Tcl's treatment of bareword literals can be frustrating to someone.
In the second case above, Tcl considers the argument to llength a list. Therefore, it is going to return the length of the list, which is equivalent to this list:
llength [list "mylist"]
DKF: The phrase "bareword literals" indicates a deviation from the Tcl Way; the concept does not really operate usefully in Tcl, unlike in a number of other languages (*cough*Perl*cough*). The llength command always works with list values, and lists are always values. If you've a list in a variable, you need to get the list out of the variable to work out its length.
LV: Technically, the problem the original writer hit isn't Tcl (as an interpreter", by llength. The documentation clearly indicates that llength takes a list as its argument. When llength looks at its argument, it sees the string mylist , which is a list - a single entry list. It sees the same way in each of these cases:
llength mylist
llength "mylist"
llength {mylist}
llength [list mylist]In each of these cases, llength sees the list/string "mylist" and NOT the value of the string.
The problem here is that some of the Tcl l* commands expect the name of a variable, while others expect the value of a variable. And it is up to the developer to keep straight the two types of requirements.
GWM Note also the slightly unexpected result for:
llength "a b c" ;# returns 3 as the string (only one string) is interpreted as a
list by llength, the spaces making 3 elements.
llength "a {b d} c" ;# is also 3 - the inner braces make a sub-list
llength {a {b d} c} ;# also 3 - it is the same as above
llength "{a {b d} c}" ;# is 1 - the braces inside the string make a sub-listAlso not the difference between braced lists and quoted in this case:
set a {a b c}
llength "1 2 $a 3" ;# 6 elements in the substituted list
llength {1 2 $a 3} ;# 4 elements in the list (which does not have $a substituted)See also list, lappend, lindex, linsert, lrange, lreplace, lsearch, lsort .
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