at_eof(+Stream)

Stream

Stream handle or alias (atom)

Description

• For file streams and string streams, this means that either the next read operation will return an end-of-file condition, or end-of-file was already read and the next read operation would result in a past-end-of-file error.
• For tty streams, it means only that there is currently no further input available, and a subsequent read operation will prompt for more.
• For queue streams, it means only that the queue is currently empty. The queue will recover from the end-of-file condition when new data is written into it from the write end.
• For pipe and socket streams, this condition means that the next read operation will either block or return an end-of-file condition. To check whether there is any data to read, use stream_select/3.
• The null stream is always at end-of-file.

Modes and Determinism

• at_eof(+) is semidet

Fail Conditions

Exceptions

(4) instantiation fault

Stream is not instantiated.

(5) type error

Stream is instantiated, but not to an atom or a stream handle.

(192) illegal stream mode

Stream is an illegal stream mode.

Examples

Success:
      at_eof(null).

      ?- open(file1,update,S), at_eof(S),
         write(S,hello), at(S,5), at_eof(S), close(S).
      yes.

Fail:

      ?- open(file1,write,S),write(S,hello), close(S),
         open(file1,read,S), at_eof(S), close(S).
      no.

Error:
      at_eof(X).                  (Error 4).
      at_eof("s").                (Error 5).
      at_eof(not_a_stream).       (Error 192).

See Also