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Asked: 2026-05-11T00:44:52+00:00

Consider the following code and its output: Code #!/usr/bin/perl -w use strict; use Data::Dumper;

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Consider the following code and its output:

Code

#!/usr/bin/perl -w use strict; use Data::Dumper; my $HOURS_PER_DAY = 24.0 * 1.0; my $BSA = 1.7 * 1.0; my $MCG_PER_MG = 1000.0 * 1.0; my $HOURS_DURATION    = 20.0 * $HOURS_PER_DAY; my $dummy = $HOURS_PER_DAY * $BSA * $MCG_PER_MG * $HOURS_DURATION; print Dumper($HOURS_PER_DAY); print Dumper( $BSA); print Dumper( $MCG_PER_MG); print Dumper( $HOURS_DURATION );

Output

$VAR1 = 24; $VAR1 = '1.7'; $VAR1 = 1000; $VAR1 = 480;

As you can see, the second variable is treated as strings, while the first and the forth ones are treated as numbers. Anybody has any idea what is the underlying logic?

Edit arithmetic calculations that were added do not completely solve the problem (see the $BSA variable).

$ perl -v  This is perl, v5.10.0 built for cygwin-thread-multi-64int (with 6 registered patches, see perl -V for more detail)  Copyright 1987-2007, Larry Wall
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1 Answer

  1. Data::Dumper’s job is to serialize data and you can’t tell much about what perl is doing internally with the data based on its output. The Devel::Peek module can dump the underlying flags and values stored in the variables. The Devel::Peek POD explains the significance of the flags.

    #!/usr/bin/perl  use warnings; use strict; use Devel::Peek;  my $HOURS_PER_DAY = 24.0 * 1.0; my $BSA = 1.7 * 1.0; my $MCG_PER_MG = 1000.0 * 1.0; my $HOURS_DURATION    = 20.0 * $HOURS_PER_DAY; my $dummy = $HOURS_PER_DAY * $BSA * $MCG_PER_MG * $HOURS_DURATION;  Dump($HOURS_PER_DAY); Dump($BSA); Dump($MCG_PER_MG); Dump($HOURS_DURATION);  __END__ SV = PVNV(0xd71ff0) at 0xd87f90   REFCNT = 1   FLAGS = (PADBUSY,PADMY,IOK,NOK,pIOK,pNOK)   IV = 24   NV = 24   PV = 0 SV = PVNV(0xd71fc8) at 0xd87f60   REFCNT = 1   FLAGS = (PADBUSY,PADMY,NOK,pIOK,pNOK)   IV = 1   NV = 1.7   PV = 0 SV = PVNV(0xd72040) at 0xd87f40   REFCNT = 1   FLAGS = (PADBUSY,PADMY,IOK,NOK,pIOK,pNOK)   IV = 1000   NV = 1000   PV = 0 SV = IV(0xd8b408) at 0xd87f30   REFCNT = 1   FLAGS = (PADBUSY,PADMY,IOK,pIOK)   IV = 480 # compare the above output to output without the assignment to $dummy: SV = IV(0x7b0eb8) at 0x7adf90   REFCNT = 1   FLAGS = (PADBUSY,PADMY,IOK,pIOK)   IV = 24 SV = NV(0x7c7c90) at 0x7adf60   REFCNT = 1   FLAGS = (PADBUSY,PADMY,NOK,pNOK)   NV = 1.7 SV = IV(0x7b13d8) at 0x7adf40   REFCNT = 1   FLAGS = (PADBUSY,PADMY,IOK,pIOK)   IV = 1000 SV = IV(0x7b1408) at 0x7adf30   REFCNT = 1   FLAGS = (PADBUSY,PADMY,IOK,pIOK)   IV = 480
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