io_lib

MODULE

io_lib

MODULE SUMMARY

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 is used for generating flat lists.

EXPORTS

nl()

Returns a character list which represents a new line character.

write(Term)
write(Term, 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:

> lists:flatten(io_lib:write({1,[2],[3],[4,5],6,7,8,9})).        
"{1,[2],[3],[4,5],6,7,8,9}"
> lists:flatten(io_lib:write({1,[2],[3],[4,5],6,7,8,9}, 5)).
"{1,[2],[3],[4|...],6|...}"

print(Term)
print(Term, Column, LineLength, 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 the maximum print depth.

fwrite(Format, Data)
format(Format, Data)

Returns a character list which represents Data formatted in accordance with Format. Refer to io 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.

fread(Format, String)

Tries to read String in accordance with the control sequences in Format. Refer to io 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}

An error occurred which can be formatted with the call format_error/1.


Example:

> io_lib:fread("~f~f~f", "15.6 17.3e-6 24.5").
{ok, [15.6000, 1.73000e-5, 24.5000], []}

fread(Continuation, CharList, Format)

This is the re-entrant formatted reader. It 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, which can be formatted with the call format_error/1.


{more, Continuation}

More data is required to build a term. Continuation must be passed to <c>fread/3, when more data becomes available.

write_atom(Atom)

Returns the list of characters needed to print the atom Atom.

write_string(String)

Returns the list of characters needed to print String as a string.

write_char(Integer)

Returns the list of characters needed to print a character constant.

indentation(String, StartIndent)

Returns the indentation if String has been printed, starting at Indentation.

char_list(CharList) -> bool()

Returns true if CharList is a list of characters, otherwise it returns false.

deep_char_list(CharList)

Returns true if CharList is a deep list of characters, otherwise it returns false.

printable_list(CharList)

Returns true if CharList is a list of printable characters, otherwise it returns false.

Notes

The module io_lib also uses the extra modules io_lib_format, io_lib_fread, and io_lib_pretty. All external interfaces exist in io_lib.

Users are strongly advised not to access the other modules directly.

Any undocumented functions in io_lib should not be used.

The continuation of the first call to the re-entrant input 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

AUTHORS

Robert Virding - support@erlang.ericsson.se