Re^2: Differences in behavior in pack

Ok, so I guess to ask a better question?

What is the difference in the way Perl stores these values? Is there away to tell the difference from a programmatic viewpoint if I am expecting hex values? What happens if the values are passed to my program either way?

$testp = 0x007102;
$testp1 = "\x30\x05\x15";
[download]

Thanks again,
Mike

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Re^3: Differences in behavior in pack by ikegami (Patriarch) on Apr 09, 2008 at 01:15 UTC
Technically, it's possible to tell the difference `>perl -MDevel::Peek; -e"Dump(0x007102)" SV = IV(0x18265fc) at 0x2252f8 REFCNT = 1 FLAGS = (PADBUSY,PADTMP,IOK,READONLY,pIOK) IV = 28930 >perl -MDevel::Peek; -e"Dump(qq{\x30\x05\x15})" SV = PV(0x226680) at 0x225300 REFCNT = 1 FLAGS = (PADBUSY,PADTMP,POK,READONLY,pPOK) <-- Not IOK/UOK/NOK PV = 0x182f6a4 "0\5\25"\0 CUR = 3 LEN = 4` [download] But checking for that would be extremely fragile. I strongly recommend against that approach. Instead, use some kind of meta data (a different command line switch, for example) to specify the format, then canonize it for internal use. `# Inputs my $input = "\x30\x05\x15"; my $packed = 1; # Canonize input if ($packed) { $input = unpack('N', substr(("\x00"x4).$input, -4)); } # Do some work #... # Output results printf("Results for 0x%X are %s\n", $input, "...");` [download] Update: Added second snippet.	[reply] [d/l] [select]

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Re^3: Differences in behavior in pack
by ikegami (Patriarch) on Apr 09, 2008 at 01:15 UTC

Technically, it's possible to tell the difference

>perl -MDevel::Peek; -e"Dump(0x007102)"
SV = IV(0x18265fc) at 0x2252f8
  REFCNT = 1
  FLAGS = (PADBUSY,PADTMP,IOK,READONLY,pIOK)
  IV = 28930

>perl -MDevel::Peek; -e"Dump(qq{\x30\x05\x15})"
SV = PV(0x226680) at 0x225300
  REFCNT = 1
  FLAGS = (PADBUSY,PADTMP,POK,READONLY,pPOK)  <-- Not IOK/UOK/NOK
  PV = 0x182f6a4 "0\5\25"\0
  CUR = 3
  LEN = 4
[download]

But checking for that would be extremely fragile. I strongly recommend against that approach. Instead, use some kind of meta data (a different command line switch, for example) to specify the format, then canonize it for internal use.

# Inputs
my $input = "\x30\x05\x15";
my $packed = 1;

# Canonize input
if ($packed) {
   $input = unpack('N', substr(("\x00"x4).$input, -4));
}

# Do some work
#...

# Output results
printf("Results for 0x%X are %s\n", $input, "...");
[download]

Update: Added second snippet.

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