Character ~ is written.

The argument is a number that is interpreted as an ASCII code. The precision is the number of times the character is printed and defaults to the field width, which in turn defaults to 1. Example:

1> io:fwrite("|~10.5c|~-10.5c|~5c|~n", [$a, $b, $c]).
|     aaaaa|bbbbb     |ccccc|
ok

If the Unicode translation modifier (t) is in effect, the integer argument can be any number representing a valid Unicode codepoint, otherwise it is to be an integer less than or equal to 255, otherwise it is masked with 16#FF:

2> io:fwrite("~tc~n",[1024]).
\x{400}
ok
3> io:fwrite("~c~n",[1024]).
^@
ok

The argument is a float that is written as [-]ddd.ddd, where the precision is the number of digits after the decimal point. The default precision is 6 and it cannot be < 1.

The argument is a float that is written as [-]d.ddde+-ddd, where the precision is the number of digits written. The default precision is 6 and it cannot be < 2.

The argument is a float that is written as f, if it is >= 0.1 and < 10000.0. Otherwise, it is written in the e format. The precision is the number of significant digits. It defaults to 6 and is not to be < 2. If the absolute value of the float does not allow it to be written in the f format with the desired number of significant digits, it is also written in the e format.

Prints the argument with the string syntax. The argument is, if no Unicode translation modifier is present, an iolist(), a binary(), or an atom(). If the Unicode translation modifier (t) is in effect, the argument is unicode:chardata(), meaning that binaries are in UTF-8. The characters are printed without quotes. The string is first truncated by the specified precision and then padded and justified to the specified field width. The default precision is the field width.

This format can be used for printing any object and truncating the output so it fits a specified field:

1> io:fwrite("|~10w|~n", [{hey, hey, hey}]).
|**********|
ok
2> io:fwrite("|~10s|~n", [io_lib:write({hey, hey, hey})]).
|{hey,hey,h|
3> io:fwrite("|~-10.8s|~n", [io_lib:write({hey, hey, hey})]).
|{hey,hey  |
ok

A list with integers > 255 is considered an error if the Unicode translation modifier is not specified:

4> io:fwrite("~ts~n",[[1024]]).
\x{400}
ok
5> io:fwrite("~s~n",[[1024]]).
** exception error: bad argument
     in function  io:format/3
        called as io:format(<0.53.0>,"~s~n",[[1024]])

Writes data with the standard syntax. This is used to output Erlang terms. Atoms are printed within quotes if they contain embedded non-printable characters. Atom characters > 255 are escaped unless the Unicode translation modifier (t) is used. Floats are printed accurately as the shortest, correctly rounded string.

Writes the data with standard syntax in the same way as ~w, but breaks terms whose printed representation is longer than one line into many lines and indents each line sensibly. Left-justification is not supported. It also tries to detect flat lists of printable characters and output these as strings. For example:

1> T = [{attributes,[[{id,age,1.50000},{mode,explicit},
{typename,"INTEGER"}], [{id,cho},{mode,explicit},{typename,'Cho'}]]},
{typename,'Person'},{tag,{'PRIVATE',3}},{mode,implicit}].
...
2> io:fwrite("~w~n", [T]).
[{attributes,[[{id,age,1.5},{mode,explicit},{typename,
[73,78,84,69,71,69,82]}],[{id,cho},{mode,explicit},{typena
me,'Cho'}]]},{typename,'Person'},{tag,{'PRIVATE',3}},{mode
,implicit}]
ok
3> io:fwrite("~62p~n", [T]).
[{attributes,[[{id,age,1.5},
               {mode,explicit},
               {typename,"INTEGER"}],
              [{id,cho},{mode,explicit},{typename,'Cho'}]]},
 {typename,'Person'},
 {tag,{'PRIVATE',3}},
 {mode,implicit}]
ok

The field width specifies the maximum line length. It defaults to 80. The precision specifies the initial indentation of the term. It defaults to the number of characters printed on this line in the same call to write/1 or format/1,2,3. For example, using T above:

4> io:fwrite("Here T = ~62p~n", [T]).
Here T = [{attributes,[[{id,age,1.5},
                        {mode,explicit},
                        {typename,"INTEGER"}],
                       [{id,cho},
                        {mode,explicit},
                        {typename,'Cho'}]]},
          {typename,'Person'},
          {tag,{'PRIVATE',3}},
          {mode,implicit}]
ok

As from Erlang/OTP 21.0, a field width of value 0 can be used for specifying that a line is infinitely long, which means that no line breaks are inserted. For example:

5> io:fwrite("~0p~n", [lists:seq(1, 30)]).
[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]
ok

When the modifier l is specified, no detection of printable character lists takes place, for example:

6> S = [{a,"a"}, {b, "b"}],
   io:fwrite("~15p~n", [S]).
[{a,"a"},
 {b,"b"}]
ok
7> io:fwrite("~15lp~n", [S]).
[{a,[97]},
 {b,[98]}]
ok

The Unicode translation modifier t specifies how to treat characters outside the Latin-1 range of codepoints, in atoms, strings, and binaries. For example, printing an atom containing a character > 255:

8> io:fwrite("~p~n",[list_to_atom([1024])]).
'\x{400}'
ok
9> io:fwrite("~tp~n",[list_to_atom([1024])]).
'Ѐ'
ok

By default, Erlang only detects lists of characters in the Latin-1 range as strings, but the +pc unicode flag can be used to change this (see printable_range/0 for details). For example:

10> io:fwrite("~p~n",[[214]]).
"Ö"
ok
11> io:fwrite("~p~n",[[1024]]).
[1024]
ok
12> io:fwrite("~tp~n",[[1024]]).
[1024]
ok

but if Erlang was started with +pc unicode:

13> io:fwrite("~p~n",[[1024]]).
[1024]
ok
14> io:fwrite("~tp~n",[[1024]]).
"Ѐ"
ok

Similarly, binaries that look like UTF-8 encoded strings are output with the binary string syntax if the t modifier is specified:

15> io:fwrite("~p~n", [<<208,128>>]).
<<208,128>>
ok
16> io:fwrite("~tp~n", [<<208,128>>]).
<<"Ѐ"/utf8>>
ok
17> io:fwrite("~tp~n", [<<128,128>>]).
<<128,128>>
ok

Writes data in the same way as ~w, but takes an extra argument that is the maximum depth to which terms are printed. Anything below this depth is replaced with .... For example, using T above:

8> io:fwrite("~W~n", [T,9]).
[{attributes,[[{id,age,1.5},{mode,explicit},{typename,...}],
[{id,cho},{mode,...},{...}]]},{typename,'Person'},
{tag,{'PRIVATE',3}},{mode,implicit}]
ok

If the maximum depth is reached, it cannot be read in the resultant output. Also, the ,... form in a tuple denotes that there are more elements in the tuple but these are below the print depth.

Writes data in the same way as ~p, but takes an extra argument that is the maximum depth to which terms are printed. Anything below this depth is replaced with ..., for example:

9> io:fwrite("~62P~n", [T,9]).
[{attributes,[[{id,age,1.5},{mode,explicit},{typename,...}],
              [{id,cho},{mode,...},{...}]]},
 {typename,'Person'},
 {tag,{'PRIVATE',3}},
 {mode,implicit}]
ok

Writes an integer in base 2-36, the default base is 10. A leading dash is printed for negative integers.

The precision field selects base, for example:

1> io:fwrite("~.16B~n", [31]).
1F
ok
2> io:fwrite("~.2B~n", [-19]).
-10011
ok
3> io:fwrite("~.36B~n", [5*36+35]).
5Z
ok

Like B, but takes an extra argument that is a prefix to insert before the number, but after the leading dash, if any.

The prefix can be a possibly deep list of characters or an atom. Example:

1> io:fwrite("~X~n", [31,"10#"]).
10#31
ok
2> io:fwrite("~.16X~n", [-31,"0x"]).
-0x1F
ok

Like B, but prints the number with an Erlang style #-separated base prefix. Example:

1> io:fwrite("~.10#~n", [31]).
10#31
ok
2> io:fwrite("~.16#~n", [-31]).
-16#1F
ok

Like B, but prints lowercase letters.

Like X, but prints lowercase letters.

Like #, but prints lowercase letters.

Writes a new line.

Ignores the next term.

The formatting succeeded.