SWI-Prolog 9.2.9 Reference Manual: Section A.6

## A.6 library(charsio): I/O on Lists of Character Codes

Compatibility
  The naming of this library is not in line with the ISO standard. We believe that the SWI-Prolog native predicates form a more elegant alternative for this library.

This module emulates the Quintus/SICStus library `charsio.pl` for reading and writing from/to lists of character codes. Most of these predicates are straight calls into similar SWI-Prolog primitives. Some can even be replaced by ISO standard predicates.

[det]format_to_chars(+Format, +Args, -Codes)
  Use format/2 to write to a list of character codes.
[det]format_to_chars(+Format, +Args, -Codes, ?Tail)
  Use format/2 to write to a difference list of character codes.
write_to_chars(+Term, -Codes)
  Write a term to a code list. True when Codes is a list of character codes written by write/1 on Term.
write_to_chars(+Term, -Codes, ?Tail)
  Write a term to a code list. Codes`\`Tail is a difference list of character codes produced by write/1 on Term.
[det]atom_to_chars(+Atom, -Codes)
  Convert Atom into a list of character codes.
  deprecated
    Use ISO atom_codes/2.
[det]atom_to_chars(+Atom, -Codes, ?Tail)
  Convert Atom into a difference list of character codes.
[det]number_to_chars(+Number, -Codes)
  Convert Atom into a list of character codes.
  deprecated
    Use ISO number_codes/2.
[det]number_to_chars(+Number, -Codes, ?Tail)
  Convert Number into a difference list of character codes.
[det]read_from_chars(+Codes, -Term)
  Read Codes into Term.
  Compatibility
    The SWI-Prolog version does not require Codes to end in a full-stop.
[det]read_term_from_chars(+Codes, -Term, +Options)
  Read Codes into Term. Options are processed by read_term/3.
  Compatibility
    sicstus
[det]open_chars_stream(+Codes, -Stream)
  Open Codes as an input stream.
  See also
    open_string/2.
[det]with_output_to_chars(:Goal, -Codes)
  Run Goal as with once/1. Output written to `current_output` is collected in Codes.
[det]with_output_to_chars(:Goal, -Codes, ?Tail)
  Run Goal as with once/1. Output written to `current_output` is collected in Codes`\`Tail.
[det]with_output_to_chars(:Goal, -Stream, -Codes, ?Tail)
  Same as with_output_to_chars/3 using an explicit stream. The difference list Codes`\`Tail contains the character codes that Goal has written to Stream.