#!/usr/bin/perl -w
use Fcntl;

# Experimenting with fcntl system call

## open this file
open( FH, ">>fcntl.pl" );

$cur_opts = fcntl( FH, &F_GETFL, 0 );
#  The print statement of death....
#  print "cur_opts -> $cur_opts\n";

$rc = fcntl( FH, &F_SETFL, $cur_opts );
# "fixes" The print statement of death...
#$rc = fcntl( FH, &F_SETFL, $cur_opts & 0xffffffff );

print "rc -> $rc\n";

$new_opts = fcntl( FH, &F_GETFL, 0 );
print "new_opts -> $new_opts\n";

if ( $new_opts != $cur_opts ) {
    print "ERROR\n";
} else {
    print "Calling F_SETFL with F_GETGL return value succeeded.\n";
}
print "new_opts -> $new_opts  cur_opts -> $cur_opts\n";

[download]
In trying to verify the proper use of fcntl (so that I can set a socket file descriptor to non-blocking), I stumbled upon the above curiosity. When I run the above code, the output generated is 
rc -> 0 but true
new_opts -> 1025
Calling F_SETFL with F_GETGL return value succeeded.
new_opts -> 1025  cur_opts -> 1025

[download]
However, if I un-comment out the "print statement of death" line (see code above), I get the following output: 
cur_opts -> 1025
rc -> 0 but true
new_opts -> 8193
ERROR
new_opts -> 8193  cur_opts -> 1025V@S@ÿÿÿÿ0ÿÿÿÿÿÿÿÿHÿÿÿÿ N@

[download]
What I want to know, then, is what crime against nature have I committed by printing out the value of $cur_opts. Or, more importantly, how can I avoid this type of problem in the future? Note that masking off the 32 low order bits in the subsequent F_SETFL call allowed me to include the print line of death. Thanks for your assistance/explanation,
Victor

Edit by tye, add CODE tags, remove BR

In reply to printing fcntl( fd, F_GETFL,0 ) return value changes its representation by weinstev

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