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NAME
io_lib - IO 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.
lists:flatten/1 can be used for flattening deep lists.
DATA 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 to true if the translation modifier t is present;
* strings is set to false if the modifier l is present.
EXPORTS
nl() -> string()
Returns a character list which represents a new line character.
write(Term) -> chars()
write(Term, Depth) -> chars()
Types:
Term = term()
Depth = depth()
Returns a character list which represents Term. The Depth (-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()
print(Term, Column, LineLength, Depth) -> chars()
Types:
Term = term()
Column = LineLength = integer() >= 0
Depth = depth()
Also returns a list of characters which represents Term, 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. Column is
the starting column (1), LineLength the maximum line length (80), and Depth (-1)
the maximum print depth.
fwrite(Format, Data) -> chars()
format(Format, Data) -> chars()
Types:
Format = io:format()
Data = [term()]
Returns a character list which represents Data formatted in accordance with Format.
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
Types:
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 String in accordance with the control sequences in Format. See
io:fread/3 for a detailed description of the available formatting options. It is
assumed that String contains whole lines. It 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 in order to complete the original
format string. RestFormat is the remaining format string, Nchars 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 the 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:
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. InputList is the list of successfully matched and read
items, and LeftOverChars are the remaining characters.
eof:
End of file has been encountered. LeftOverChars are the input characters not
used.
{error, What}:
An error occurred and the 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.
write_atom(Atom) -> chars()
Types:
Atom = atom()
Returns the list of characters needed to print the atom Atom.
write_string(String) -> chars()
Types:
String = string()
Returns the list of characters needed to print String as a string.
write_string_as_latin1(String) -> latin1_string()
Types:
String = string()
Returns the list of characters needed to print String as a string. Non-Latin-1
characters are escaped.
write_latin1_string(Latin1String) -> latin1_string()
Types:
Latin1String = latin1_string()
Returns the list of characters needed to print Latin1String as a string.
write_char(Char) -> chars()
Types:
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()
Types:
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()
Types:
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
Types:
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}
Types:
FormatList = [char() | format_spec()]
Format = io:format()
Data = [term()]
See io_lib:scan_format/2 for details.
build_text(FormatList) -> chars()
Types:
FormatList = [char() | format_spec()]
See io_lib:scan_format/2 for details.
indentation(String, StartIndent) -> integer()
Types:
String = string()
StartIndent = integer()
Returns the indentation if String has been printed, starting at StartIndent.
char_list(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a flat list of characters in the Unicode range, otherwise
it returns false.
latin1_char_list(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a flat list of characters in the ISO-latin-1 range,
otherwise it returns false.
deep_char_list(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a, possibly deep, list of characters in the Unicode range,
otherwise it returns false.
deep_latin1_char_list(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a, possibly deep, list of characters in the ISO-latin-1
range, otherwise it returns false.
printable_list(Term) -> boolean()
Types:
Term = term()
Returns true if Term 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()
Types:
Term = term()
Returns true if Term is a flat list of printable ISO-latin-1 characters, otherwise
it returns false.
printable_unicode_list(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a flat list of printable Unicode characters, otherwise it
returns false.