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authorRichard Carlsson <[email protected]>2018-03-02 17:01:22 +0100
committerRichard Carlsson <[email protected]>2018-03-08 12:33:10 +0100
commit437943f77f3fb9d2a12c659e52c8d35e3e24fbc6 (patch)
tree7218c675bcfdec8c4361ff98b50273e07673029c /lib
parentbd5ebce131cc8a02e559b8eec2a68b089ca235a6 (diff)
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Improve documentation of io:format ~p when Unicode is involved
Diffstat (limited to 'lib')
-rw-r--r--lib/stdlib/doc/src/io.xml72
1 files changed, 53 insertions, 19 deletions
diff --git a/lib/stdlib/doc/src/io.xml b/lib/stdlib/doc/src/io.xml
index 72c774e6ef..6a7c06188b 100644
--- a/lib/stdlib/doc/src/io.xml
+++ b/lib/stdlib/doc/src/io.xml
@@ -167,11 +167,11 @@ ok</pre>
The default padding character is <c>' '</c> (space).</p>
</item>
<item>
- <p><c>Mod</c> is the control sequence modifier. It is either a
- single character (<c>t</c>, for Unicode
- translation, and <c>l</c>, for stopping <c>p</c> and
- <c>P</c> from detecting printable characters)
- that changes the interpretation of <c>Data</c>.</p>
+ <p><c>Mod</c> is the control sequence modifier. It is a
+ single character that changes the interpretation of
+ <c>Data</c>. This can be <c>t</c>, for Unicode translation,
+ or <c>l</c>, for stopping <c>p</c> and <c>P</c> from
+ detecting printable characters.</p>
</item>
</list>
<p><em>Available control sequences:</em></p>
@@ -277,10 +277,9 @@ ok
<c>~w</c>, 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 lists of
- printable characters and to output these as strings. The
- Unicode translation modifier is used for determining
- what characters are printable, for example:</p>
+ It also tries to detect flat lists of
+ printable characters and output these as strings.
+ For example:</p>
<pre>
1> <input>T = [{attributes,[[{id,age,1.50000},{mode,explicit},</input>
<input>{typename,"INTEGER"}], [{id,cho},{mode,explicit},{typename,'Cho'}]]},</input>
@@ -302,7 +301,7 @@ ok
{mode,implicit}]
ok</pre>
<p>The field width specifies the maximum line length.
- Defaults to 80. The precision specifies the initial
+ 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 <em>same</em> call to
<seealso marker="#write/1"><c>write/1</c></seealso> or
@@ -332,18 +331,53 @@ ok
[{a,[97]},
{b,[98]}]
ok</pre>
- <p>Binaries that look like UTF-8 encoded strings are
- output with the string syntax if the Unicode translation
- modifier is specified:</p>
+ <p>The Unicode translation modifier <c>t</c> 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 &gt; 255:</p>
+ <pre>
+8> <input>io:fwrite("~p~n",[list_to_atom([1024])]).</input>
+'\x{400}'
+ok
+9> <input>io:fwrite("~tp~n",[list_to_atom([1024])]).</input>
+'Ѐ'
+ok</pre>
+ <p>By default, Erlang only detects lists of characters
+ in the Latin-1 range as strings, but the <c>+pc unicode</c>
+ flag can be used to change this (see <seealso
+ marker="#printable_range/0">
+ <c>printable_range/0</c></seealso> for details). For example:</p>
+ <pre>
+10> <input>io:fwrite("~p~n",[[214]]).</input>
+"Ö"
+ok
+11> <input>io:fwrite("~p~n",[[1024]]).</input>
+[1024]
+ok
+12> <input>io:fwrite("~tp~n",[[1024]]).</input>
+[1024]
+ok
+</pre>
+ <p>but if Erlang was started with <c>+pc unicode</c>:</p>
<pre>
-9> <input>io:fwrite("~p~n",[[1024]]).</input>
+13> <input>io:fwrite("~p~n",[[1024]]).</input>
[1024]
-10> <input>io:fwrite("~tp~n",[[1024]]).</input>
-"\x{400}"
-11> <input>io:fwrite("~tp~n", [&lt;&lt;128,128&gt;&gt;]).</input>
+ok
+14> <input>io:fwrite("~tp~n",[[1024]]).</input>
+"Ѐ"
+ok</pre>
+ <p>Similarly, binaries that look like UTF-8 encoded strings
+ are output with the binary string syntax if the <c>t</c>
+ modifier is specified:</p>
+ <pre>
+15> <input>io:fwrite("~p~n", [&lt;&lt;208,128&gt;&gt;]).</input>
+&lt;&lt;208,128&gt;&gt;
+ok
+16> <input>io:fwrite("~tp~n", [&lt;&lt;208,128&gt;&gt;]).</input>
+&lt;&lt;"Ѐ"/utf8&gt;&gt;
+ok
+17> <input>io:fwrite("~tp~n", [&lt;&lt;128,128&gt;&gt;]).</input>
&lt;&lt;128,128&gt;&gt;
-12> <input>io:fwrite("~tp~n", [&lt;&lt;208,128&gt;&gt;]).</input>
-&lt;&lt;"\x{400}"/utf8&gt;&gt;
ok</pre>
</item>
<tag><c>W</c></tag>