Question

From this question:

bytearray – Perl pack/unpack and length of binary string – Stack Overflow

I’ve learned that @unparray = unpack("d "x5, $aa); in the snippet below results with string items in the unparray – not with double precision numbers (as I expected).

Is it possible to somehow obtain an array of double-precision values from the $aa bytestring in the snippet below?:

$a = pack("d",255);
print length($a)."\n";
# prints 8

$aa = pack("ddddd", 255,123,0,45,123);
print length($aa)."\n";
# prints 40

@unparray = unpack("d "x5, $aa);
print scalar(@unparray)."\n";
# prints 5

print length($unparray[0])."\n" 
# prints 3

printf "%d\n", $unparray[0] '
# prints 255

# one liner:
# perl -e '$a = pack("d",255); print length($a)."\n"; $aa = pack("ddddd", 255,123,0,45,123); print length($aa)."\n"; @unparray = unpack("d "x5, $aa); print scalar(@unparray)."\n"; print length($unparray[0])."\n" '

Many thanks in advance for any answers,
Cheers!

Answer 1

What makes you think it’s not stored as a double?

use feature qw( say );

use Config      qw( %Config );
use Devel::Peek qw( Dump );

my @a = unpack "d5", pack "d5", 255,123,0,45,123;

say 0+@a;             # 5
Dump $a[0];           # NOK (floating point format)
say $Config{nvsize};  # 8 byte floats on this build