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NAME

       io_lib - I/O library functions.

DESCRIPTION

       This  module  contains functions for converting to and from strings (lists of characters).
       They are used for implementing the functions in the io module. There is no guarantee  that
       the  character lists returned from some of the functions are flat, they can be deep lists.
       Function lists:flatten/1 can be used for flattening deep lists.

DATA TYPES

       chars() = [char() | chars()]

       continuation()

              A continuation as returned by fread/3.

       chars_limit() = integer()

       depth() = -1 | integer() >= 0

       fread_error() =
           atom | based | character | float | format | input | integer |
           string | unsigned

       fread_item() = string() | atom() | integer() | float()

       latin1_string() = [unicode:latin1_char()]

       format_spec() =
           #{control_char := char(),
             args := [any()],
             width := none | integer(),
             adjust := left | right,
             precision := none | integer(),
             pad_char := char(),
             encoding := unicode | latin1,
             strings := boolean()}

              Where:

                * control_char is the type of control sequence: $P, $w, and so on.

                * args is a list of the arguments used by the control sequence, or an empty  list
                  if the control sequence does not take any arguments.

                * width is the field width.

                * adjust is the adjustment.

                * precision is the precision of the printed argument.

                * pad_char is the padding character.

                * encoding is set to true if translation modifier t is present.

                * strings is set to false if modifier l is present.

EXPORTS

       build_text(FormatList) -> chars()

              Types:

                 FormatList = [char() | format_spec()]

              For details, see scan_format/2.

       char_list(Term) -> boolean()

              Types:

                 Term = term()

              Returns  true  if Term is a flat list of characters in the Unicode range, otherwise
              false.

       deep_char_list(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a, possibly deep, list of characters in the Unicode  range,
              otherwise false.

       deep_latin1_char_list(Term) -> boolean()

              Types:

                 Term = term()

              Returns  true  if  Term  is a, possibly deep, list of characters in the ISO Latin-1
              range, otherwise false.

       format(Format, Data) -> chars()

       fwrite(Format, Data) -> chars()

              Types:

                 Format = io:format()
                 Data = [term()]

              Returns a character list that represents Data formatted in accordance with  Format.
              For   a   detailed   description   of   the   available   formatting  options,  see
              io:fwrite/1,2,3. If the format string or argument list contains an error,  a  fault
              is generated.

              If  and only if the Unicode translation modifier is used in the format string (that
              is, ~ts or ~tc), the resulting list can contain characters beyond the  ISO  Latin-1
              character  range  (that  is, numbers > 255). If so, the result is still an ordinary
              Erlang string(), and can well be used in any context where Unicode data is allowed.

       format(Format, Data, Options) -> chars()

       fwrite(Format, Data, Options) -> chars()

              Types:

                 Format = io:format()
                 Data = [term()]
                 Options = [Option]
                 Option = {chars_limit, CharsLimit}
                 CharsLimit = chars_limit()

              Returns a character list that represents Data formatted in accordance  with  Format
              in  the  same  way as fwrite/2 and format/2, but takes an extra argument, a list of
              options.

              Valid option:

                {chars_limit, CharsLimit}:
                  A soft limit  on  the  number  of  characters  returned.  When  the  number  of
                  characters  is  reached, remaining structures are replaced by "...". CharsLimit
                  defaults to -1, which means no limit on the number of characters returned.

       fread(Format, String) -> Result

              Types:

                 Format = String = string()
                 Result =
                     {ok, InputList :: [fread_item()], LeftOverChars :: string()} |
                     {more,
                      RestFormat :: string(),
                      Nchars :: integer() >= 0,
                      InputStack :: chars()} |
                     {error, {fread, What :: fread_error()}}

              Tries to read String in accordance with the control  sequences  in  Format.  For  a
              detailed  description  of  the  available formatting options, see io:fread/3. It is
              assumed that String contains whole lines.

              The function returns:

                {ok, InputList, LeftOverChars}:
                  The string was read. InputList is the list of  successfully  matched  and  read
                  items, and LeftOverChars are the input characters not used.

                {more, RestFormat, Nchars, InputStack}:
                  The  string  was read, but more input is needed to complete the original format
                  string. RestFormat is the remaining format string,  Nchars  is  the  number  of
                  characters scanned, and InputStack is the reversed list of inputs matched up to
                  that point.

                {error, What}:
                  The read operation failed and parameter What gives a hint about the error.

              Example:

              3> io_lib:fread("~f~f~f", "15.6 17.3e-6 24.5").
              {ok,[15.6,1.73e-5,24.5],[]}

       fread(Continuation, CharSpec, Format) -> Return

              Types:

                 Continuation = continuation() | []
                 CharSpec = string() | eof
                 Format = string()
                 Return =
                     {more, Continuation1 :: continuation()} |
                     {done, Result, LeftOverChars :: string()}
                 Result =
                     {ok, InputList :: [fread_item()]} |
                     eof |
                     {error, {fread, What :: fread_error()}}

              This is the re-entrant formatted reader. The continuation of the first call to  the
              functions must be []. For a complete description of how the re-entrant input scheme
              works, see  Armstrong,  Virding,  Williams:  'Concurrent  Programming  in  Erlang',
              Chapter 13.

              The function returns:

                {done, Result, LeftOverChars}:
                  The input is complete. The result is one of the following:

                  {ok, InputList}:
                    The  string  was read. InputList is the list of successfully matched and read
                    items, and LeftOverChars are the remaining characters.

                  eof:
                    End of file was encountered. LeftOverChars are the input characters not used.

                  {error, What}:
                    An error occurred and parameter What gives a hint about the error.

                {more, Continuation}:
                  More data is required to build a term. Continuation must be passed  to  fread/3
                  when more data becomes available.

       indentation(String, StartIndent) -> integer()

              Types:

                 String = string()
                 StartIndent = integer()

              Returns the indentation if String has been printed, starting at StartIndent.

       latin1_char_list(Term) -> boolean()

              Types:

                 Term = term()

              Returns  true  if  Term  is  a  flat  list  of characters in the ISO Latin-1 range,
              otherwise false.

       nl() -> string()

              Returns a character list that represents a new line character.

       print(Term) -> chars()

       print(Term, Column, LineLength, Depth) -> chars()

              Types:

                 Term = term()
                 Column = LineLength = integer() >= 0
                 Depth = depth()

              Returns a list of characters  that  represents  Term,  but  breaks  representations
              longer  than one line into many lines and indents each line sensibly. Also tries to
              detect and output lists of printable characters as strings.

                * Column is the starting column; defaults to 1.

                * LineLength is the maximum line length; defaults to 80.

                * Depth is the maximum print depth; defaults to -1, which means no limitation.

       printable_latin1_list(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a flat list of printable ISO Latin-1 characters,  otherwise
              false.

       printable_list(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a flat list of printable characters, otherwise false.

              What is a printable character in this case is determined by startup flag +pc to the
              Erlang VM; see io:printable_range/0 and erl(1).

       printable_unicode_list(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a flat list  of  printable  Unicode  characters,  otherwise
              false.

       scan_format(Format, Data) -> FormatList

              Types:

                 Format = io:format()
                 Data = [term()]
                 FormatList = [char() | format_spec()]

              Returns  a  list  corresponding  to  the  specified  format  string,  where control
              sequences have been replaced with corresponding tuples. This list can be passed to:

                * build_text/1 to have the same effect as format(Format, Args)

                * unscan_format/1 to get the corresponding pair of Format and Args (with every  *
                  and corresponding argument expanded to numeric values)

              A  typical use of this function is to replace unbounded-size control sequences like
              ~w and ~p with the depth-limited variants ~W and ~P before formatting to  text  in,
              for example, a logger.

       unscan_format(FormatList) -> {Format, Data}

              Types:

                 FormatList = [char() | format_spec()]
                 Format = io:format()
                 Data = [term()]

              For details, see scan_format/2.

       write(Term) -> chars()

       write(Term, Depth) -> chars()

       write(Term, Options) -> chars()

              Types:

                 Term = term()
                 Options = [Option]
                 Option =
                     {chars_limit, CharsLimit} |
                     {depth, Depth} |
                     {encoding, latin1 | utf8 | unicode}
                 CharsLimit = chars_limit()
                 Depth = depth()

              Returns  a  character list that represents Term. Option Depth controls the depth of
              the structures written. When the specified depth is reached, everything below  this
              level is replaced by "...". Depth defaults to -1, which means no limitation. Option
              CharsLimit puts a soft limit on the number of characters returned. When the  number
              of  characters  is  reached, remaining structures are replaced by "...". CharsLimit
              defaults to -1, which means no limit on the number of characters returned.

              Example:

              1> lists:flatten(io_lib:write({1,[2],[3],[4,5],6,7,8,9})).
              "{1,[2],[3],[4,5],6,7,8,9}"
              2> lists:flatten(io_lib:write({1,[2],[3],[4,5],6,7,8,9}, 5)).
              "{1,[2],[3],[...],...}"
              3> lists:flatten(io_lib:write({[1,2,3],[4,5],6,7,8,9}, [{chars_limit,20}])).
              "{[1,2|...],[4|...],...}"

       write_atom(Atom) -> chars()

              Types:

                 Atom = atom()

              Returns the list of characters needed to print atom Atom.

       write_atom_as_latin1(Atom) -> latin1_string()

              Types:

                 Atom = atom()

              Returns the list of characters needed to print atom  Atom.  Non-Latin-1  characters
              are escaped.

       write_char(Char) -> chars()

              Types:

                 Char = char()

              Returns  the list of characters needed to print a character constant in the Unicode
              character set.

       write_char_as_latin1(Char) -> latin1_string()

              Types:

                 Char = char()

              Returns the list of characters needed to print a character constant in the  Unicode
              character set. Non-Latin-1 characters are escaped.

       write_latin1_char(Latin1Char) -> latin1_string()

              Types:

                 Latin1Char = unicode:latin1_char()

              Returns  the  list  of  characters  needed to print a character constant in the ISO
              Latin-1 character set.

       write_latin1_string(Latin1String) -> latin1_string()

              Types:

                 Latin1String = latin1_string()

              Returns the list of characters needed to print Latin1String as a string.

       write_string(String) -> chars()

              Types:

                 String = string()

              Returns the list of characters needed to print String as a string.

       write_string_as_latin1(String) -> latin1_string()

              Types:

                 String = string()

              Returns the list of characters needed to print  String  as  a  string.  Non-Latin-1
              characters are escaped.