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
Functions
For details, see scan_format/2.
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.
Equivalent to fwrite(Format, Data).
Equivalent to fwrite(Format, Data, Options).
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 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.
Equivalent to print(Term, 1, 80, -1).
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
For details, see scan_format/2.
Equivalent to write(Term, -1).
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
An possibly deep list containing only char/0s.
-type chars_limit() :: integer().
-opaque continuation()
A continuation as returned by fread/3.
-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_charis the type of control sequence:$P,$w, and so on.argsis a list of the arguments used by the control sequence, or an empty list if the control sequence does not take any arguments.widthis the field width.adjustis the adjustment.precisionis the precision of the printed argument.pad_charis the padding character.encodingis set totrueif translation modifiertis present.stringsis set tofalseif modifierlis present.maps_orderis set toundefinedby default,orderedif modifierkis present, orreversedorCmpFunif modifierKis present.
-type fread_error() :: atom | based | character | float | format | input | integer | string | unsigned.
-type latin1_string() :: [unicode:latin1_char()].
Functions
-spec build_text(FormatList) -> chars() when FormatList :: [char() | format_spec()].
For details, see scan_format/2.
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.
Equivalent to fwrite(Format, Data).
-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.InputListis the list of successfully matched and read items, andLeftOverCharsare the input characters not used.{more, RestFormat, Nchars, InputStack}- The string was read, but more input is needed to complete the original format string.RestFormatis the remaining format string,Ncharsis the number of characters scanned, andInputStackis the reversed list of inputs matched up to that point.{error, What}- The read operation failed and parameterWhatgives 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],[]}
-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.InputListis the list of successfully matched and read items, andLeftOverCharsare the remaining characters.eof- End of file was encountered.LeftOverCharsare the input characters not used.{error, What}- An error occurred and parameterWhatgives a hint about the error.
{more, Continuation}- More data is required to build a term.Continuationmust be passed tofread/3when more data becomes available.
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.
-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 "...".CharsLimitdefaults to -1, which means no limit on the number of characters returned.
-spec indentation(String, StartIndent) -> integer() when String :: string(), StartIndent :: integer().
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.
-spec nl() -> string().
Returns a character list that represents a new line character.
Equivalent to print(Term, 1, 80, -1).
-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.
Columnis the starting column; defaults to 1.LineLengthis the maximum line length; defaults to 80.Depthis the maximum print depth; defaults to -1, which means no limitation.
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.
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).
Returns true if Term is a flat list of printable Unicode characters,
otherwise false.
-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:
build_text/1to have the same effect asformat(Format, Args)unscan_format/1to get the corresponding pair ofFormatandArgs(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.
-spec unscan_format(FormatList) -> {Format, Data} when FormatList :: [char() | format_spec()], Format :: io:format(), Data :: [term()].
For details, see scan_format/2.
Equivalent to write(Term, -1).
-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|...],...}"
Returns the list of characters needed to print atom Atom.
-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.
Returns the list of characters needed to print a character constant in the Unicode character set.
-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.
-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.
-spec write_latin1_string(Latin1String) -> latin1_string() when Latin1String :: latin1_string().
Returns the list of characters needed to print Latin1String as a string.
Returns the list of characters needed to print String as a string.
-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.