void h12ascii (TH1* h)
{
   Int_t n = h->GetNbinsX();

   for (Int_t i=1; i<=n; i++) {
      printf("%g %g\n",
             h->GetBinLowEdge(i)+h->GetBinWidth(i)/2,
             h->GetBinContent(i));
   }
}

root [0] .x h12ascii.C(hpx); > h2ascii.dat