[U]

[..]
  1. UCHAR_MAX
  2. UESP
  3. UINT_MAX
  4. ULONG_MAX
  5. USED
  6. USHRT_MAX
  7. UTS_MACHINE
  8. UTS_NODENAME
  9. UTS_RELEASE
  10. UTS_SYSNAME
  11. UTS_VERSION
[..]