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), but 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.
I suspect that caspian was just frustrated that Tcl doesn't require you to have something around mylist to indicate that it is data. Many other languages require data to be deliminated by quotes of some sort. The fact that single word strings (i.e. bareword literals) are permitted in Tcl can be frustrating for people (even old-timers....).
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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