Module
io_lib
Module Summary
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 totrue
if translation modifiert
is present. -
strings
is set tofalse
if modifierl
is present.
Exports
build_text(FormatList) -> chars() | OTP 18.0 |
Types
For details, see scan_format/2
.
char_list(Term) -> boolean() |
Types
Returns true
if Term
is a flat list of characters in the Unicode range, otherwise false
.
deep_char_list(Term) -> boolean() |
Types
Returns true
if Term
is a, possibly deep, list of characters in the Unicode range, otherwise false
.
deep_latin1_char_list(Term) -> boolean() | OTP R16B |
Types
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
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() | OTP 21.0 |
fwrite(Format, Data, Options) -> chars() | OTP 21.0 |
Types
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
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, andLeftOverChars
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, andInputStack
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
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, andLeftOverChars
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 tofread/3
when more data becomes available.
indentation(String, StartIndent) -> integer() |
Types
Returns the indentation if String
has been printed, starting at StartIndent
.
latin1_char_list(Term) -> boolean() | OTP R16B |
Types
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
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() | OTP R16B |
Types
Returns true
if Term
is a flat list of printable ISO Latin-1 characters, otherwise false
.
printable_list(Term) -> boolean() |
Types
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() | OTP R16B |
Types
Returns true
if Term
is a flat list of printable Unicode characters, otherwise false
.
scan_format(Format, Data) -> FormatList | OTP 18.0 |
Types
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} | OTP 18.0 |
Types
For details, see scan_format/2
.
write(Term) -> chars() |
write(Term, Depth) -> chars() |
write(Term, Options) -> chars() | OTP 20.0 |
Types
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
Returns the list of characters needed to print atom Atom
.
write_atom_as_latin1(Atom) -> latin1_string() | OTP 20.0 |
Types
Returns the list of characters needed to print atom Atom
. Non-Latin-1 characters are escaped.
write_char(Char) -> chars() |
Types
Returns the list of characters needed to print a character constant in the Unicode character set.
write_char_as_latin1(Char) -> latin1_string() | OTP R16B |
Types
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() | OTP R16B |
Types
Returns the list of characters needed to print a character constant in the ISO Latin-1 character set.
write_latin1_string(Latin1String) -> latin1_string() | OTP R16B |
Types
Returns the list of characters needed to print Latin1String
as a string.
write_string(String) -> chars() |
Types
Returns the list of characters needed to print String
as a string.
write_string_as_latin1(String) -> latin1_string() | OTP R16B |
Types
Returns the list of characters needed to print String
as a string. Non-Latin-1 characters are escaped.
© 2010–2020 Ericsson AB
Licensed under the Apache License, Version 2.0.