read_string/3

Availability:built-in

read_string(+Stream, ?Length, -String)

Read at most Length characters from Stream and return them in the string String. If Length is unbound, Stream is read to the end and Length is unified with the number of characters read. The number of bytes read depends on the encoding of Stream (see section 2.18.1). This predicate may be used to read a sequence of bytes when the stream is in octet encoding. See open/4 and set_stream/2 for controlling the encoding.

Examples

Read all lines to a list

file_lines(File, Lines) :-
    setup_call_cleanup(open(File, read, In),
       stream_lines(In, Lines),
       close(In)).

stream_lines(In, Lines) :-
    read_string(In, _, Str),
    split_string(Str, "\n", "", Lines).

This loads all lines to memory as strings. If we use the Unix dictionary words:

?- file_lines("/usr/share/dict/words", Lines).
Words = ["A", "a", "aa", "aal", "aalii", "aam", "Aani", "aardvark", "aardwolf"|...].