Maybe this will clarify things a little.

This constructs a union between a unsigned 32-bit integer and a struct containing 32 x 1-bit fields.

It assigned the value 0x01234567 to the uint and then prints (from C) a string of 0s & 1s to reflect the bitfields, first to last in the struct.

You'll notice from the output (after __END__), that the first bitfield in the struct maps to the lsb in the integer; and the last to the msb; indicating that this is a little-endian (intel) machine.

It then passes the uint back to perl, packs it using the little-endian template 'V' and unpacks its bits using both 'b' and 'B'.

Note that the 'b' template mirrors the ordering of the bits as seen via the bitfields.

However, once you go beyond that into the realms of C++ coercions and bitsets, I'm afraid your on your own.

#! perl -slw
use strict;
use Inline C => Config => BUILD_NOISY => 1,;
use Inline C => <<'END_C',  NAME => 'bitfields', CLEAN_AFTER_BUILD =>0
+;

#include "mytypes.h"

union {
    struct {
        unsigned b00:1; unsigned b01:1; unsigned b02:1; unsigned b03:1
+;
        unsigned b04:1; unsigned b05:1; unsigned b06:1; unsigned b07:1
+;
        unsigned b08:1; unsigned b09:1; unsigned b10:1; unsigned b11:1
+;
        unsigned b12:1; unsigned b13:1; unsigned b14:1; unsigned b15:1
+;
        unsigned b16:1; unsigned b17:1; unsigned b18:1; unsigned b19:1
+;
        unsigned b20:1; unsigned b21:1; unsigned b22:1; unsigned b23:1
+;
        unsigned b24:1; unsigned b25:1; unsigned b26:1; unsigned b27:1
+;
        unsigned b28:1; unsigned b29:1; unsigned b30:1; unsigned b31:1
+;
    } bits;
    U32 uint;
} X;

U32 test( SV *unused ) {
    X.uint = 0x01234567;

    printf( "%u\n", X.uint );
    printf( "%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%
+c%c%c%c\n",
      X.bits.b00 ? '1' : '0', X.bits.b01 ? '1' : '0', X.bits.b02 ? '1'
+ : '0',
      X.bits.b03 ? '1' : '0', X.bits.b04 ? '1' : '0', X.bits.b05 ? '1'
+ : '0',
      X.bits.b06 ? '1' : '0', X.bits.b07 ? '1' : '0', X.bits.b08 ? '1'
+ : '0',
      X.bits.b09 ? '1' : '0', X.bits.b10 ? '1' : '0', X.bits.b11 ? '1'
+ : '0',
      X.bits.b12 ? '1' : '0', X.bits.b13 ? '1' : '0', X.bits.b14 ? '1'
+ : '0',
      X.bits.b15 ? '1' : '0', X.bits.b16 ? '1' : '0', X.bits.b17 ? '1'
+ : '0',
      X.bits.b18 ? '1' : '0', X.bits.b19 ? '1' : '0', X.bits.b20 ? '1'
+ : '0',
      X.bits.b21 ? '1' : '0', X.bits.b22 ? '1' : '0', X.bits.b23 ? '1'
+ : '0',
      X.bits.b24 ? '1' : '0', X.bits.b25 ? '1' : '0', X.bits.b26 ? '1'
+ : '0',
      X.bits.b27 ? '1' : '0', X.bits.b28 ? '1' : '0', X.bits.b29 ? '1'
+ : '0',
      X.bits.b30 ? '1' : '0', X.bits.b31 ? '1' : '0'
    );
    return X.uint;
}

END_C

my $uint = test( 1 );
print unpack 'b*', pack 'V', $uint;
print unpack 'B*', pack 'V', $uint;

__END__
C:\test>bitFields.pl
19088743
11100110101000101100010010000000
11100110101000101100010010000000
01100111010001010010001100000001
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