How to check if list element exists in TCL?

list tcl exists
Narek picture Narek · Apr 11, 2011 · Viewed 33.2k times · Source

Say I have a TCL list, and I have append some elements to my list. Now I want to check if I have appended 6 or 7 elements.

In order to check if list element exists in the place specified by an index I have used:

if { [info exists [lindex $myList 6]] } {
#if I am here then I have appended 7 elems, otherwise it should be at least 6
}

But seams this does not work. How I should do that? properly? It is OK to check if { [lindex $myList 6]] eq "" }

Answer

überjesus picture überjesus · Apr 11, 2011

Why don't you use llength to check the length of your list:

if {[llength $myList] == 6} {
    # do something
}

Of course, if you want to check the element at a specific index, then then use lindex to retrieve that element and check that. e.g. if {[lindex $myList 6] == "something"}

Your code using the info exists is not working, because the info exists command checks if a variable exists. So you are basically checking if there is a variable whose name equals the value returned by [lindex $myList 6].

Related questions

TCL remove an element from a list

How te remove an element from TCL list say: which has index = 4 which has value = "aa" I have Googled and have not found any built-in function yet.

Read More
Passing list to Tcl procedure

What is the canonical way to pass a list to a Tcl procedure? I'd really like it if I could get it so that a list is automatically expanded into a variable number of arguments. So that something like: set …

Read More
What does {*} do in TCL?

I have used some TCL, but this construction stumps me. When $res = "Table does not exist", what will the following return? [list [list {*}$res]] I know what [list [list $res]] would do, but the extra {*} just baffles me. Thanks for …

Read More