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
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
|
<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 288721 $ -->
<sect1 xml:id="language.types.boolean">
<title>Booleans</title>
<simpara>
This is the simplest type. A <type>boolean</type> expresses a truth value. It
can be either &true; or &false;.
</simpara>
<note>
<simpara>
The <type>boolean</type> type was introduced in PHP 4.
</simpara>
</note>
<sect2 xml:id="language.types.boolean.syntax">
<title>Syntax</title>
<para>
To specify a <type>boolean</type> literal, use the keywords &true; or
&false;. Both are case-insensitive.
</para>
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
$foo = True; // assign the value TRUE to $foo
?>
]]>
</programlisting>
</informalexample>
<para>
Typically, some kind of <link linkend="language.operators">operator</link>
which returns a <type>boolean</type> value, and the value is passed on to a
<link linkend="language.control-structures">control structure</link>.
</para>
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
// == is an operator which test
// equality and returns a boolean
if ($action == "show_version") {
echo "The version is 1.23";
}
// this is not necessary...
if ($show_separators == TRUE) {
echo "<hr>\n";
}
// ...because instead, this can be used:
if ($show_separators) {
echo "<hr>\n";
}
?>
]]>
</programlisting>
</informalexample>
</sect2>
<sect2 xml:id="language.types.boolean.casting">
<title>Converting to boolean</title>
<simpara>
To explicitly convert a value to <type>boolean</type>, use the
<literal>(bool)</literal> or <literal>(boolean)</literal> casts. However, in
most cases the cast is unncecessary, since a value will be automatically
converted if an operator, function or control structure requires a
<type>boolean</type> argument.
</simpara>
<simpara>
See also <link linkend="language.types.type-juggling">Type Juggling</link>.
</simpara>
<para>
When converting to <type>boolean</type>, the following values are considered
&false;:
</para>
<itemizedlist>
<listitem>
<simpara>
the <link linkend="language.types.boolean">boolean</link> &false; itself
</simpara>
</listitem>
<listitem>
<simpara>
the <link linkend="language.types.integer">integer</link> 0 (zero)
</simpara>
</listitem>
<listitem>
<simpara>
the <link linkend="language.types.float">float</link> 0.0 (zero)
</simpara>
</listitem>
<listitem>
<simpara>
the empty <link linkend="language.types.string">string</link>, and the
<link linkend="language.types.string">string</link> "0"
</simpara>
</listitem>
<listitem>
<simpara>
an <link linkend="language.types.array">array</link> with zero elements
</simpara>
</listitem>
<listitem>
<simpara>
an <link linkend="language.types.object">object</link> with zero member
variables (PHP 4 only)
</simpara>
</listitem>
<listitem>
<simpara>
the special type <link linkend="language.types.null">NULL</link> (including
unset variables)
</simpara>
</listitem>
<listitem>
<simpara>
<link linkend="ref.simplexml">SimpleXML</link> objects created from empty
tags
</simpara>
</listitem>
</itemizedlist>
<para>
Every other value is considered &true; (including any
<link linkend="language.types.resource">resource</link>).
</para>
<warning>
<simpara>
<literal>-1</literal> is considered &true;, like any other non-zero
(whether negative or positive) number!
</simpara>
</warning>
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
var_dump((bool) ""); // bool(false)
var_dump((bool) 1); // bool(true)
var_dump((bool) -2); // bool(true)
var_dump((bool) "foo"); // bool(true)
var_dump((bool) 2.3e5); // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array()); // bool(false)
var_dump((bool) "false"); // bool(true)
?>
]]>
</programlisting>
</informalexample>
</sect2>
</sect1>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"~/.phpdoc/manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->
|
