io_lib
IO 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. lists:flatten/1
can be used for
flattening deep lists.
Types
chars() = [char() | chars()]
continuation()
A continuation as returned by fread/3
.
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()}
Description:
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 the translation modifiert
is present;strings
is set tofalse
if the modifierl
is present.
Functions
nl() -> string()
Returns a character list which represents a new line character.
write(Term) -> chars()
Term = term()
write(Term, Depth) -> chars()
Term = term()
Depth = depth()
Returns a character list which represents
. The
(-1) argument controls the depth of the
structures written. When the specified depth is reached,
everything below this level is replaced by "...". For
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],[...],...}"
print(Term) -> chars()
Term = term()
print(Term, Column, LineLength, Depth) -> chars()
Term = term()
Column = LineLength = integer() >= 0
Depth = depth()
Also returns a list of characters which represents
, but breaks representations which are longer than
one line into many lines and indents each line sensibly. It
also tries to detect and output lists of printable characters
as strings.
is the starting column (1),
the maximum line length (80), and
(-1) the maximum print depth.
fwrite(Format, Data) -> chars()
Format = io:format()
Data = [term()]
format(Format, Data) -> chars()
Format = io:format()
Data = [term()]
Returns a character list which represents
formatted in accordance with
. See
io:fwrite/1,2,3 for a detailed
description of the available formatting options. A fault is
generated if there is an error in the format string or
argument list.
If (and only if) the Unicode translation modifier is used in the format string (i.e. ~ts or ~tc), the resulting list may contain characters beyond the ISO-latin-1 character range (in other words, numbers larger than 255). If so, the result is not an ordinary Erlang string(), but can well be used in any context where Unicode data is allowed.
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
. See
io:fread/3 for a detailed
description of the available formatting options. It is
assumed that
contains whole lines. It 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 in order
to complete the original format string.
is the remaining format string,
the number
of characters scanned, and
is the
reversed list of inputs matched up to that point.
{error, What }
The read operation failed and the 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 []
. Refer to
Armstrong, Virding, Williams, 'Concurrent Programming in
Erlang', Chapter 13 for a complete description of how the
re-entrant input scheme works.
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 has been encountered.
are the input characters not
used.
{error, What }
An error occurred and the 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.
write_atom(Atom) -> chars()
Atom = atom()
Returns the list of characters needed to print the atom
.
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.
write_latin1_string(Latin1String) -> latin1_string()
Latin1String = latin1_string()
Returns the list of characters needed to print
as a string.
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.
scan_format(Format, Data) -> FormatList
Format = io:format()
Data = [term()]
FormatList = [char() | format_spec()]
Returns a list corresponding to the given format string,
where control sequences have been replaced with
corresponding tuples. This list can be passed to io_lib:build_text/1 to have
the same effect as io_lib:format(Format, Args)
, or to
io_lib:unscan_format/1
in order 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, e.g. in a logger.
unscan_format(FormatList) -> {Format, Data}
FormatList = [char() | format_spec()]
Format = io:format()
Data = [term()]
See io_lib:scan_format/2 for details.
build_text(FormatList) -> chars()
FormatList = [char() | format_spec()]
See io_lib:scan_format/2 for details.
indentation(String, StartIndent) -> integer()
String = string()
StartIndent = integer()
Returns the indentation if
has been printed,
starting at
.
char_list(Term) -> boolean()
Term = term()
Returns true
if
is a flat list of
characters in the Unicode range, otherwise it returns false
.
latin1_char_list(Term) -> boolean()
Term = term()
Returns true
if
is a flat list of
characters in the ISO-latin-1 range, otherwise it returns false
.
deep_char_list(Term) -> boolean()
Term = term()
Returns true
if
is a, possibly deep, list
of characters in the Unicode range, otherwise it returns 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 it returns false
.
printable_list(Term) -> boolean()
Term = term()
Returns true
if
is a flat list of
printable characters, otherwise it returns false
.
What is a printable character in this case is determined by the
+pc
start up flag to the Erlang VM. See
io:printable_range/0
and erl(1).
printable_latin1_list(Term) -> boolean()
Term = term()
Returns true
if
is a flat list of
printable ISO-latin-1 characters, otherwise it returns false
.
printable_unicode_list(Term) -> boolean()
Term = term()
Returns true
if
is a flat list of
printable Unicode characters, otherwise it returns false
.