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lset(n) Tcl Built-In Commands lset(n)
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NAME
lset - Change an element in a list
SYNOPSIS
lset varName ?index...? newValue
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DESCRIPTION
The lset command accepts a parameter, varName, which it interprets as the name of a vari-
able containing a Tcl list. It also accepts zero or more indices into the list. The
indices may be presented either consecutively on the command line, or grouped in a Tcl
list and presented as a single argument. Finally, it accepts a new value for an element
of varName.
If no indices are presented, the command takes the form:
lset varName newValue
or
lset varName {} newValue
In this case, newValue replaces the old value of the variable varName.
When presented with a single index, the lset command treats the content of the varName
variable as a Tcl list. It addresses the index'th element in it (0 refers to the first
element of the list). When interpreting the list, lset observes the same rules concerning
braces and quotes and backslashes as the Tcl command interpreter; however, variable sub-
stitution and command substitution do not occur. The command constructs a new list in
which the designated element is replaced with newValue. This new list is stored in the
variable varName, and is also the return value from the lset command.
If index is negative or greater than or equal to the number of elements in $varName, then
an error occurs.
The interpretation of each simple index value is the same as for the command string index, |
supporting simple index arithmetic and indices relative to the end of the list.
If additional index arguments are supplied, then each argument is used in turn to address
an element within a sublist designated by the previous indexing operation, allowing the
script to alter elements in sublists. The command,
lset a 1 2 newValue
or
lset a {1 2} newValue
replaces element 2 of sublist 1 with newValue.
The integer appearing in each index argument must be greater than or equal to zero. The
integer appearing in each index argument must be strictly less than the length of the cor-
responding list. In other words, the lset command cannot change the size of a list. If
an index is outside the permitted range, an error is reported.
EXAMPLES
In each of these examples, the initial value of x is:
set x [list [list a b c] [list d e f] [list g h i]]
-> {a b c} {d e f} {g h i}
The indicated return value also becomes the new value of x (except in the last case, which
is an error which leaves the value of x unchanged.)
lset x {j k l}
-> j k l
lset x {} {j k l}
-> j k l
lset x 0 j
-> j {d e f} {g h i}
lset x 2 j
-> {a b c} {d e f} j
lset x end j
-> {a b c} {d e f} j
lset x end-1 j
-> {a b c} j {g h i}
lset x 2 1 j
-> {a b c} {d e f} {g j i}
lset x {2 1} j
-> {a b c} {d e f} {g j i}
lset x {2 3} j
-> list index out of range
In the following examples, the initial value of x is:
set x [list [list [list a b] [list c d]] \
[list [list e f] [list g h]]]
-> {{a b} {c d}} {{e f} {g h}}
The indicated return value also becomes the new value of x.
lset x 1 1 0 j
-> {{a b} {c d}} {{e f} {j h}}
lset x {1 1 0} j
-> {{a b} {c d}} {{e f} {j h}}
SEE ALSO
list(n), lappend(n), lindex(n), linsert(n), llength(n), lsearch(n), lsort(n), lrange(n),
lreplace(n), string(n) |
KEYWORDS
element, index, list, replace, set
Tcl 8.4 lset(n)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
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