package CParsingThingy;

sub new {
  my $class=shift;
  my $self={};
  # you could either do this...
  $self->{program}={};
  # or this:
  # $self->{functions}=[];
  # $self->{typedefs}=[];
  # $self->{defined_in}={};
  # etc.
  bless $self, $class;
}

...

sub parse_program {
  my $self=shift;
  my $source=shift;
  my $program=$self->{program};
  # and use $program as before.
  ..
}

# etc.