William wrote:
>> use strict;
>> use warnings;
>>
>> use Devel::Peek qw/Dump/;
>>
>> my $numstr = sprintf("%4d", 1234);
>> Dump $numstr;
>>
>> $numstr = sprintf("%05d", 1234);
>> Dump $numstr;
>>
>> my $num = sprintf("%05d", 1234);
>> $num += 0;
>> Dump $num;
>>
>> **OUTPUT**
>>
>> SV = PV(0x365ec) at 0x3652c
>> REFCNT = 1
>> FLAGS = (PADBUSY,PADMY,POK,pPOK)
>> PV = 0x182ea94 "1234"\0
>> CUR = 4
>> LEN = 8
>> SV = PV(0x365ec) at 0x3652c
>> REFCNT = 1
>> FLAGS = (PADBUSY,PADMY,POK,pPOK)
>> PV = 0x182ea94 "01234"\0
>> CUR = 5
>> LEN = 8
>> SV = PVIV(0x37604) at 0x357c4
>> REFCNT = 1
>> FLAGS = (PADBUSY,PADMY,IOK,pIOK)
>> IV = 1234
>> PV = 0x183ba74 "01234"\0
>> CUR = 5
>> LEN = 8
>>
>> So in the first two cases you can see that the POK flag (denoting a string
>> value) is set, but in the third case, after adding zero, the IOK flag becomes
>> set (indicating an integer) while the POK flag is cleared, meaning that the
>> the
>> string value is no longer valid, even though there is still space allocated
>> for
>> it and its value is unchanged.
>
> Thank you, now it's very clear to me. So scalar variable might look very
> flexible to our programmer's eyes as it can contain either integer or string,
> but I never know what is happening behind the scene until you show me that
> one.
> It create a big problem to me when I did not convert it to integer first
> before
> getting into the SWI-Prolog . Because Perl string means atom in SWI-Prolog,
> only
> Perl number means number in SWI-Prolog.
My apologies, I'm afraid we lost track of your purpose. My best advice is to
force the value to numeric or string at the point of call and *comment* it so
that it doesn't look like a mistake.
my $ypm = '17'.'60';
dbase_function($ypm+0); # Call requires a numeric value
or
my $index = sprintf '%05d', $n;
dbase_function("$index"); # Call requires a string value
HTH,
Rob
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