Packing to a file

Instead of packing to a buffer, and subsequently storing data to a file, you can directly pack to a file by passing the filename and openmode arguments to pack or xdr_pack's constructor. The arguments are identical to that of fopen:

 {
  pack_t checkpoint("foo.ckpt","w");
  checkpoint << bar;
 }

The advantage here is large checkpoints can be written to disk without intermediate buffering in memory. The file is closed when the pack_t object is destroyed.