C99 says that CHAR_BIT must be at least 8; POSIX says it must be exactly 8; on Windows it's 8. That's about all the platforms it's worth caring about.

Some DSPs use CHAR_BIT=16 or CHAR_BIT=32, but they're never going to run Perl anyway.

How to get it? This is cheating I'm sure...

use strict;
use warnings;

my $char_bit;
open my $fh, "<", "/usr/include/limits.h";
while (<$fh>) {
    ($char_bit = $1, last) if /^#\s*define\s*CHAR_BIT\s*([0-9]+)/;
}

print "$char_bit\n";
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It's the kind of detail you might expect to be provided by Config, but no such luck :-(

Update: meh... I wasn't looking hard enough...

use strict;
use warnings;
use Config;

print "$Config{charbits}\n";
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Oh indeed. New Config piece starting from 5.12, this is why I didn't see it.
Read more... (3 kB)

This isn't addressing specifically how Perl is compiled, but rather how Perl implements the notion of characters: Because of Perl's Unicode implementation, a Perl character isn't necessarily a single byte. Consider the following:

binmode STDOUT, ':encoding(utf8)';
my $cp = "\x{3a3}";
print "$cp\n"; # Prints an upper case sigma.
print ord( $cp ), "\n"; # prints 931.
print 0x00FF & ord( $cp ), "\n"; # prints 163.
if( ord( $cp ) > 255 ) {
    print "Wide character.\n";
}
if( ord( $cp ) != ( 0x00FF & ord( $cp ) ) ) {
    print "Wide character.\n";
}
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If you're not dropping into XS, what application is there for getting at the actual value of CHAR_BIT during compilation? (Just to satisfy my own curiosity, and to learn something new).

Update: To be more clear in my final question: I do understand that the C implementation could possibly be compiled with CHAR_BIT != 8. We see checks for it within the XS code of Scalar::Vec::Util and Math::MPC, for example. But what I'm curious about is how it makes any difference from the perspective of a Perl script that doesn't use XS (aside from the potential that some XS modules will break because they're not checking like they should).

No particular reason other than completeness. I am adding a larger set of exportable constants to Devel::PeekPoke::Constants and wanted to be as thorough as possible ;)

As far as why care about C stuff if you are not in C land - well again Devel::PeekPoke.

Cheers

Making Devel::PeekPoke::Constants more thorough is a great reason! :)




Dave

$ perl "-V:.*?char.*?"
charbits='8';
d_charvspr='undef';
stdchar='char';

Not so fast. See http://www.perlmonks.org/?node_id=1022456