FILES

  errno.map        - Contains list of errno names specified by POSIX. Second
                     field is a brief description of the value
                     (ignored by compilation).

  errno_to_ada.map - Contains mapping of errno names to Ada Error_t
                     values.

  errno_to_int.map - Generated by errno_to_int.sh. Contains mapping of errno
                     names to integer values on the current system.

DESCRIPTION

  A mapping is specified from POSIX errno names to an enumerated Ada type
  (Error_t). An enumerated type is used in preference of individual constants
  to allow static checking of case values ("have I handled all possible
  error conditions appropriately?").

  All values of Error_t are prefixed with 'Error_' to help avoid namespace
  pollution.

  A function is provied to map a given Error_t value to a system-specific
  POSIX errno value:

    function Errno_To_Ada (Value : in Error_t) return Interfaces.C.int;

  In order to retrieve error messages for Error_t values, it is necessary
  to convert Error_t back to a system-specific integer value in order to
  pass the value to a message catalogue of locale-specific messages.

  A function is provided to map a given POSIX errno value to an Ada Error_t
  value:

    function Ada_To_Errno (Value : in Interfaces.C.int) return Error_t;

IMPLEMENTATION

  Values of POSIX errno names are not guaranteed to be consistent across
  systems or distinct on any given system. The values of the set of POSIX
  errno names are discovered at compile time and written to errno_to_int.map.

  Both Error_t<->POSIX errno mapping functions are generated at compile time
  using the definitions in errno.map and errno_to_ada.map.