View Source io_lib (stdlib v6.0)

I/O library functions.

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.

Summary

Types

An possibly deep list containing only char/0s.

A continuation as returned by fread/3.

A map describing the contents of a format string.

Functions

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

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

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

Tries to read String in accordance with the control sequences in Format.

This is the re-entrant formatted reader. The continuation of the first call to the functions must be [].

Returns a character list that represents Data formatted in accordance with Format.

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.

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

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

Returns a character list that represents a new line character.

Returns a list of characters that represents Term, but breaks representations longer than one line into many lines and indents each line sensibly.

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

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

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

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

Returns a character list that represents Term. Option Depth controls the depth of the structures written.

Returns the list of characters needed to print atom Atom.

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

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

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

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

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

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

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

Types

-type chars() :: [char() | chars()].

An possibly deep list containing only char/0s.

-type chars_limit() :: integer().
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continuation()

View Source (opaque)
-opaque continuation()

A continuation as returned by fread/3.

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depth()

View Source (not exported)
-type depth() :: -1 | non_neg_integer().
-type format_spec() ::
    #{control_char := char(),
      args := [any()],
      width := none | integer(),
      adjust := left | right,
      precision := none | integer(),
      pad_char := char(),
      encoding := unicode | latin1,
      strings := boolean(),
      maps_order => maps:iterator_order()}.

A map describing the contents of a format string.

  • 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.
  • maps_order is set to undefined by default, ordered if modifier k is present, or reversed or CmpFun if modifier K is present.
-type fread_error() :: atom | based | character | float | format | input | integer | string | unsigned.
-type fread_item() :: string() | atom() | integer() | float().
-type latin1_string() :: [unicode:latin1_char()].

Functions

Link to this function

build_text(FormatList)

View Source (since OTP 18.0)
-spec build_text(FormatList) -> chars() when FormatList :: [char() | format_spec()].

For details, see scan_format/2.

-spec char_list(Term) -> boolean() when Term :: term().

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

-spec deep_char_list(Term) -> boolean() when Term :: term().

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

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deep_latin1_char_list(Term)

View Source (since OTP R16B)
-spec deep_latin1_char_list(Term) -> boolean() when Term :: term().

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

-spec format(Format, Data) -> chars() when Format :: io:format(), Data :: [term()].

Equivalent to fwrite(Format, Data)

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format(Format, Data, Options)

View Source (since OTP 21.0)
-spec format(Format, Data, Options) -> chars()
          when
              Format :: io:format(),
              Data :: [term()],
              Options :: [Option],
              Option :: {chars_limit, CharsLimit},
              CharsLimit :: chars_limit().

Equivalent to fwrite(Format, Data, Options)

-spec fread(Format, String) -> Result
         when
             Format :: string(),
             String :: string(),
             Result ::
                 {ok, InputList :: [fread_item()], LeftOverChars :: string()} |
                 {more,
                  RestFormat :: string(),
                  Nchars :: non_neg_integer(),
                  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],[]}
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fread(Continuation, CharSpec, Format)

View Source
-spec fread(Continuation, CharSpec, Format) -> Return
         when
             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.

-spec fwrite(Format, Data) -> chars() when 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/0, and can well be used in any context where Unicode data is allowed.

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fwrite(Format, Data, Options)

View Source (since OTP 21.0)
-spec fwrite(Format, Data, Options) -> chars()
          when
              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.
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indentation(String, StartIndent)

View Source
-spec indentation(String, StartIndent) -> integer() when String :: string(), StartIndent :: integer().

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

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latin1_char_list(Term)

View Source (since OTP R16B)
-spec latin1_char_list(Term) -> boolean() when Term :: term().

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

-spec nl() -> string().

Returns a character list that represents a new line character.

-spec print(Term) -> chars() when Term :: term().

Equivalent to print(Term, 1, 80, -1)

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print(Term, Column, LineLength, Depth)

View Source
-spec print(Term, Column, LineLength, Depth) -> chars()
         when
             Term :: term(),
             Column :: non_neg_integer(),
             LineLength :: non_neg_integer(),
             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.
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printable_latin1_list(Term)

View Source (since OTP R16B)
-spec printable_latin1_list(Term) -> boolean() when Term :: term().

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

-spec printable_list(Term) -> boolean() when 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).

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printable_unicode_list(Term)

View Source (since OTP R16B)
-spec printable_unicode_list(Term) -> boolean() when Term :: term().

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

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scan_format(Format, Data)

View Source (since OTP 18.0)
-spec scan_format(Format, Data) -> FormatList
               when
                   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:

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.

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unscan_format(FormatList)

View Source (since OTP 18.0)
-spec unscan_format(FormatList) -> {Format, Data}
                 when
                     FormatList :: [char() | format_spec()],
                     Format :: io:format(),
                     Data :: [term()].

For details, see scan_format/2.

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write(Term)

View Source (since OTP 20.0)
-spec write(Term) -> chars() when Term :: term().

Equivalent to write(Term, -1)

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write(Term, DepthOrOptions)

View Source (since OTP 20.0)
-spec write(Term, Depth) -> chars() when Term :: term(), Depth :: depth();
     (Term, Options) -> chars()
         when
             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|...],...}"
-spec write_atom(Atom) -> chars() when Atom :: atom().

Returns the list of characters needed to print atom Atom.

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write_atom_as_latin1(Atom)

View Source (since OTP 20.0)
-spec write_atom_as_latin1(Atom) -> latin1_string() when Atom :: atom().

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

-spec write_char(Char) -> chars() when Char :: char().

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

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write_char_as_latin1(Char)

View Source (since OTP R16B)
-spec write_char_as_latin1(Char) -> latin1_string() when Char :: char().

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

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write_latin1_char(Latin1Char)

View Source (since OTP R16B)
-spec write_latin1_char(Latin1Char) -> latin1_string() when Latin1Char :: unicode:latin1_char().

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

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write_latin1_string(Latin1String)

View Source (since OTP R16B)
-spec write_latin1_string(Latin1String) -> latin1_string() when Latin1String :: latin1_string().

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

-spec write_string(String) -> chars() when String :: string().

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

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write_string_as_latin1(String)

View Source (since OTP R16B)
-spec write_string_as_latin1(String) -> latin1_string() when String :: string().

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