Here's my interim solution: 
package HErrno;

# tlhackque - roughly based on a scheme by Perlbotics 
# in http://www.perlmonks.org/index.pl?node_id=773351
#
# use HErrno.pm;
#
# print $herrno{$?}              # String from h_errno
# print $herrno{NETDB_SUCCESS}   # String from name or value

# use HErrno.pm qw( :NAMES );    # Constant (subroutines) for all name
+s
# use HErrno.pm qw ( HOST_NOT_FOUND ); # Constant for one name
#
# my h_errno = $?
# if( h_errno == HOST_NOT_FOUND ) ...
# 
our (@EXPORT, @EXPORT_OK,%EXPORT_TAGS,@ISA,%herrno,$VERSION);
use Exporter ();
use strict;

$VERSION = "0.01_00";
$VERSION = eval $VERSION;

@ISA = qw(Exporter);

@EXPORT = qw(%herrno);

BEGIN {
    %herrno = (
           # Symbols to obtain => error string to return.
           NETDB_INTERNAL => "See errno.",
           NETDB_SUCCESS  => "No problem.",
           HOST_NOT_FOUND => "Authoritative Answer Host not found.",
           TRY_AGAIN      => "Non-Authoritative Host not found, or SER
+VERFAIL.",
           NO_RECOVERY    => "Non recoverable errors, FORMERR, REFUSED
+, NOTIMP.",
           NO_DATA        => "Valid name, no data record of requested 
+type.",
           NO_ADDRESS     => "No address, look for MX record.",
           );
    @EXPORT_OK = ( qw(NO_ADDRESS) );
    %EXPORT_TAGS = (
            NAMES => [qw(NO_ADDRESS)]
            );

    # Get symbol values from netdb.h.  This isn't robust...

    open my $errdb, '<', '/usr/include/netdb.h' or die;

    while (my $line = <$errdb>) {
    if (my ($symbol, $val) = $line =~ /^\s*\#\s*define\s+([^_]\w+)\s+(
+-?\d+)/) {
        next unless exists $herrno{$symbol}; # skip irrelevant symbols
        die "FATAL: $symbol = $val - conflicts with  $herrno{$val}\n"
        if exists $herrno{$val};
        # Map numeric codes to text strings
        $herrno{$val} = $herrno{$symbol};
        # Provide a symbolic value
        { no strict 'refs' ;
          *{$symbol} = sub () { $val; };
        }
        # Export the symbol & add to the NAMES tag
        push @EXPORT_OK, $symbol;
        push @{$EXPORT_TAGS{NAMES}}, $symbol;
    }
    }

    # NO_ADDRESS is an alias for NO_DATA
    sub NO_ADDRESS() { NO_DATA() };
    
    close $errdb or die;    
}

1;
__END__

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This communication may not represent my employer's views, if any, on the matters discussed.

In reply to Re: h_errno constants? by tlhackque
in thread h_errno constants? by tlhackque

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