What follows doesn't involve a lot of code, but demonstrates some nice things you can do with Perl's powerful. flexible, concise syntax. It is something I used in a project of mine where I am genearating a lot of C++ code.

The code generates a large number of source and header files. In its first incarnation, each file was just opened and closed as needed, like this:

open SRC "> file";
# print lots of stuff
close SRC;
[download]

This was fine for a while, but as time went on the thing got slower and slower, as the number of files grew. Also the sounds coming out of the hard disc suggested that some optimisation was in order. Hmm.

So here's a wish list for some improvements;

• keep a number of files open, get back the filehandles as needed by the program by a simple mechanism.
• Minimise opening and closing of file handles.
• Provide a simple way to print header and footer text in the file (e.g. the guard statements which are necessary in CPP header files).
• Clean up nicely when done. This means closing file handles, and calling methods that handle version management software as needed.

Here's how it was done:

{
    my %fhs;

    sub END
    {
    foreach (keys %fhs)
    {
        my $fh = $fhs{$_};

        if ($_ =~ /\.h\.new$/)
        {
        print $fh "#endif\n";
        }
        close $fh;
        if ($_ =~ /\.h\.new$/)
        {
          Clearcase::handleClearCaseElement($_);
        }
    }
    }

sub openFile
{
    my ($file, $header) = @_;
    
    unless (defined $fhs{$file})
    {
    my $f;
    open ($f, "> $file") || die "could not open $file for output $!";
    $fhs{$file} = $f;
    print $f $header;
    }
    return $fhs{$file};
}

}
[download]

It's pretty simple. The END block handles cleanup, adds closing #ENDIFs where necessary, and calls some Clearcase handling routines which take care of version control.. The %fhs hash is private to the END and openFile methods. openFile takes an argument for header info for the file in my system. You could change this around to fit your requirements.

The other code has an easy time now. Whenever a certain file is wanted for output, just call my $fh = openFile('myFilename.cc', $header) and start printing to $fh. Job done.

The script is back down to a few seconds to run as a result of this (from over 30 seconds) and the disc is a lot happier. The code is much more readable too.

It would be wise, if the number of files gets very high, to extend this code to check that the number of open filehandles does not get too close to the system limit. It's possible to see some smart mechanism where least used filehandles are closed and only reopened when requested again ... as I don't need this right now, I'll leave this as an exercise for some future monk ...

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.