TCL use a variable to contain list of arguments for format command

[Keith McLeod]

Trying to set up list to format using format specifiers.  Looking to have it be dynamic in building the specifiers and the value list to format.

set listLen 3 – works

set fmt “%-40.40s %-7.7s [lrepeat $listLen \%\-10\.10s]” – works

puts [format $fmt “A” “B” “C” “D” “E”] – works

Since the number of specifiers is 5, is there a way to use a variable for the values like

set valList {“A” “B” “C” “D” “E”} – works

puts [format $fmt $valList] – Doesn’t work

Error: not enough arguments for all format specifiers

I must be overlooking the obvious.  Any ideas or help is appreciated….

Topic

[David Barr]

The “format” command expects separate arguments, not a list. You can use this syntax:

puts [format $fmt {*}$valList]

The “{*}” syntax expands the list into separate arguments to a command.

[Charlie Bursell]

Good catch David.  Not a lot of people using the {*} syntax in Cloverleaf but it a very valuable command for your toolbox.  It was added in Tcl 8.5.  See below for usage and examples.

https://wiki.tcl-lang.org/page/%7B%2A%7D

 

[David Barr]

The “{*}” syntax explains how to write this the way you originally proposed, but I thought of another way to do this that may be simpler. Instead of dynamically building the format string and using that to generate the output string, it may be easier to dynamically generate the output string. Something like this:

set v1 A
set v2 B
set valList { C D E }
set outVal [format “%-40.40s %-7.7s ” $v1 $v2]
foreach v $valList {
append outVal [format “%-10.10s” $v]
}
puts $outVal

• This reply was modified 3 years, 11 months ago by David Barr.
• This reply was modified 3 years, 11 months ago by David Barr.

[Charlie Bursell]

Lots of ways in Tcl to do the same things.  For example:

set fmt “%-40.40s %-7.7s %-10.10s %-10.10s %-10.10s”
set valList “A  B  C  D  E”
set cmd {format $fmt}

foreach var $valList {set cmd [concat $cmd $var]}

echo [eval $cmd]

I would still prefer the {*} paradigm.

The {*} was created because eval can be a pain at times

[Author]

Replies