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.
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 totrue
if translation modifiert
is present.strings
is set tofalse
if modifierl
is present.
Functions
build_text(FormatList) -> chars()
FormatList = [char() | format_spec()]
For details, see
scan_format/2
.
char_list(Term) -> boolean()
Term = term()
Returns true
if
is a flat list of
characters in the Unicode range, otherwise false
.
deep_char_list(Term) -> boolean()
Term = term()
Returns true
if
is a, possibly deep,
list of characters in the Unicode range, otherwise false
.
deep_latin1_char_list(Term) -> boolean()
Term = term()
Returns true
if
is a, possibly deep,
list of characters in the ISO Latin-1 range, otherwise
false
.
format(Format, Data) -> chars()
Format = io:format()
Data = [term()]
fwrite(Format, Data) -> chars()
Format = io:format()
Data = [term()]
Returns a character list that represents
formatted in accordance with
.
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()
Format = io:format()
Data = [term()]
Options = [Option]
Option = {chars_limit, CharsLimit}
CharsLimit = chars_limit()
fwrite(Format, Data, Options) -> chars()
Format = io:format()
Data = [term()]
Options = [Option]
Option = {chars_limit, CharsLimit}
CharsLimit = chars_limit()
Returns a character list that represents
formatted in accordance with
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 "...
".
defaults to -1, which
means no limit on the number of characters returned.
fread(Format, String) -> Result
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
in accordance with the
control sequences in
.
For a detailed description of the available formatting options, see
io:fread/3
. It is
assumed that
contains whole lines.
The function returns:
{ok, InputList ,
LeftOverChars }
The string was read.
is the list
of successfully matched and read items, and
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.
is the
remaining format string,
is the number
of characters scanned, and
is the
reversed list of inputs matched up to that point.
{error, What }
The read operation failed and parameter
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
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.
is the
list of successfully matched and read items, and
are the remaining
characters.
eof
End of file was encountered.
are the input characters not
used.
{error, What }
An error occurred and parameter
gives a hint about the error.
{more, Continuation }
More data is required to build a term.
must be passed to fread/3
when more data becomes available.
indentation(String, StartIndent) -> integer()
String = string()
StartIndent = integer()
Returns the indentation if
has been
printed, starting at
.
latin1_char_list(Term) -> boolean()
Term = term()
Returns true
if
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()
Term = term()
print(Term, Column, LineLength, Depth) -> chars()
Term = term()
Column = LineLength = integer() >= 0
Depth = depth()
Returns a list of characters that represents
, 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.
is the starting column; defaults to 1.Column
is the maximum line length; defaults to 80.LineLength
is the maximum print depth; defaults to -1, which means no limitation.Depth
printable_latin1_list(Term) -> boolean()
Term = term()
Returns true
if
is a flat list of
printable ISO Latin-1 characters, otherwise false
.
printable_list(Term) -> boolean()
Term = term()
Returns true
if
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()
Term = term()
Returns true
if
is a flat list of
printable Unicode characters, otherwise false
.
scan_format(Format, Data) -> FormatList
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 asformat(Format, Args)
-
unscan_format/1
to get the corresponding pair ofFormat
andArgs
(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}
FormatList = [char() | format_spec()]
Format = io:format()
Data = [term()]
For details, see
scan_format/2
.
write(Term) -> chars()
Term = term()
Returns a character list that represents
.
Option
controls the depth of the
structures written. When the specified depth is reached,
everything below this level is replaced by "...
".
defaults to -1, which means
no limitation. Option
puts a
soft limit on the number of characters returned. When the
number of characters is reached, remaining structures are
replaced by "...
".
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_as_latin1(Atom) -> latin1_string()
Atom = atom()
Returns the list of characters needed to print atom
. Non-Latin-1 characters
are escaped.
write_char(Char) -> chars()
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()
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()
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()
Latin1String = latin1_string()
Returns the list of characters needed to print
as a string.
write_string(String) -> chars()
String = string()
Returns the list of characters needed to print
as a string.
write_string_as_latin1(String) -> latin1_string()
String = string()
Returns the list of characters needed to print
as a string. Non-Latin-1
characters are escaped.