Getting fixed width columnar output using 'printf' in Perl [duplicate] - perl

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Closed 10 years ago.
Possible Duplicate:
Formatting output with 'printf' in Perl
my #selections = ("Hamburger","Frankfurter","French Fries","Large Coke","Medium Coke","Small Coke","Onion Rings");
my #prices = (3.49, 2.19, 1.69, 1.79, 1.59, 1.39, 1.19);
my #quantity = (3, 0, 0, 4, 0, 0, 8);
printf("%s %10s %12s %10s\n", "Qty", "Desc.", "Unit \$", "Total");
for($meh = 0; $meh <= 6; $meh++)
{
if($quantity[$meh] != 0)
{
printf("%d %10s %9.2f %7.2f\n", $quantity[$meh], $selections[$meh], $prices[$meh], $prices[$meh]*$quantity[$meh])
}
}
I can't figure out how to make the columns line up. I followed the suggestions of another post, but it still isn't working.

Answer 1

The problem is that your strings are more than 10 characters long, and Perl won't cut them unless you specify a maximum width, which is given after the dot for strings (%10.10s). Also, you may want to use a negative number so they become aligned to the left (%-10.10s).

Answer 2

If you want the columns to be exactly aligned based on dynamic input data, you need to make two passes over the rows. The first time through, record the maximum length of each column. Then construct a format string using those lengths. Finally, print each row using that format string.
use strict;
use warnings;
my #selections = ("Hamburger","Frankfurter","French Fries","Large Coke","Medium Coke","Small Coke","Onion Rings");
my #prices = (3.49, 2.19, 1.69, 1.79, 1.59, 1.39, 1.19);
my #quantity = (3, 0, 0, 4, 0, 0, 8);
my #rows;
push #rows, ["Qty", "Desc.", "Unit \$", "Total"];
# construct table data as a two-dimensional array
for (my $meh = 0; $meh < #selections; $meh++) {
next unless $quantity[$meh];
push #rows, [$quantity[$meh], $selections[$meh], $prices[$meh], $prices[$meh]*$quantity[$meh]];
}
# first pass over rows: compute the maximum width for each column
my #widths;
for my $row (#rows) {
for (my $col = 0; $col < #$row; $col++) {
$widths[$col] = length $row->[$col] if length $row->[$col] > ($widths[$col] // 0);
}
}
# compute the format. for this data, it works out to "%-3s %-11s %-6s %-5s\n"
my $format = join(' ', map { "%-${_}s" } #widths) . "\n";
# second pass: print each row using the format
for my $row (#rows) {
printf $format, #$row;
}
That yields this output:
Qty Desc. Unit $ Total
3 Hamburger 3.49 10.47
4 Large Coke 1.79 7.16
8 Onion Rings 1.19 9.52

Answer 3

Long time ago, Perl was mainly used for formatting files. It still has this capabilities although I haven't seen it used in a program since Perl 4.x came out.
Check out the perlform documentation, the format function, and the write function.
I'd give you an example on what the code would look like except I haven't done it in years. Otherwise, use the printf statement. You can limit the size of a text field with a %-10.10s type of format. This says to left justify the string, and pad it out to 10 characters, but not more than 10 characters.
I also suggest you get a book on modern Perl. One that will teach you about references.
I've rewritten your program to use references. Notice that all of the data is now in a single array instead of spread over four separate arrays that you hope you keep the index together.
I can talk about the ENTREE of $item[1] by saying $item[1]->{ENTREE}. It's easier to read and easier to maintain.
Also note that I've changed your for loop. In yours, you had to know that you had seven items. If you added a new item, you'd have to change your loop. In mine, I use $#menu to get the last index of my menu. I then use (0..$#menu) to automatically loop from 0 to the last item in the #menu array.
use strict;
use warnings;
use Data::Dumper;
my #menu = (
{ ENTREE => "Hamburger", PRICE => 3.49, QUANTITY => 3 },
{ ENTREE => "Frankfurter", PRICE => 2.19, QUANTITY => 0 },
{ ENTREE => "French Fries", PRICE => 1.69, QUANTITY => 0 },
{ ENTREE => "Large Coke", PRICE => 1.79, QUANTITY => 4 },
{ ENTREE => "Medium Coke", PRICE => 1.59, QUANTITY => 0 },
{ ENTREE => "Small Coke", PRICE => 1.39, QUANTITY => 0 },
{ ENTREE => "Onion Rings", PRICE => 1.19, QUANTITY => 8 },
);
printf "%-3.3s %-10.10s %-6.6s %s\n\n", 'Qty', 'Desc.', 'Unit $', 'Total';
# Use $#menu to get the number of items in the array instead of knowing it's 6
foreach my $item (0..$#menu) {
# Dereference $menu[$item] to make $menu_item a hash
# This makes the syntax easier to read.
my %menu_item = %{ $menu[$item] };
if ( $menu_item{QUANTITY} ) {
printf "%3d %-10.10s %9.2f %7.2f\n",
$menu_item{QUANTITY}, $menu_item{ENTREE}, $menu_item{PRICE},
$menu_item{QUANTITY} * $menu_item{PRICE};
}
}
OUTPUT:
Qty Desc. Unit $ Total
3 Hamburger 3.49 10.47
4 Large Coke 1.79 7.16
8 Onion Ring 1.19 9.52