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><A
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>Hoofdstuk 6. Types</TD
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><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="language.types.boolean"
>Booleans</A
></H1
><P
> This is the easiest type. A <A
HREF="language.types.boolean.html"
><B
CLASS="type"
>boolean</B
></A
> expresses a
truth value. It can be either <TT
CLASS="constant"
><B
>TRUE</B
></TT
> or <TT
CLASS="constant"
><B
>FALSE</B
></TT
>.
</P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Opmerking: </B
>
The boolean type was introduced in PHP 4.
</P
></BLOCKQUOTE
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="language.types.boolean.syntax"
>Syntax</A
></H2
><P
> To specify a boolean literal, use either the keyword <TT
CLASS="constant"
><B
>TRUE</B
></TT
>
or <TT
CLASS="constant"
><B
>FALSE</B
></TT
>. Both are case-insensitive.
<DIV
CLASS="informalexample"
><P
></P
><A
NAME="AEN2348"
></A
><TABLE
BORDER="0"
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><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br />$foo </font><font color="#007700">= </font><font color="#0000BB">True</font><font color="#007700">; </font><font color="#FF8000">// assign the value TRUE to $foo<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> Usually you
use some kind of <A
HREF="language.operators.html"
>operator</A
>
which returns a <A
HREF="language.types.boolean.html"
><B
CLASS="type"
>boolean</B
></A
> value, and then pass it
on to a <A
HREF="missing-stuff.html#language.control-structures"
>control
structure</A
>.
<DIV
CLASS="informalexample"
><P
></P
><A
NAME="AEN2354"
></A
><TABLE
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><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#FF8000">// == is an operator which test<br />// equality and returns a boolean<br /></font><font color="#007700">if (</font><font color="#0000BB">$action </font><font color="#007700">== </font><font color="#DD0000">"show_version"</font><font color="#007700">) {<br /> echo </font><font color="#DD0000">"The version is 1.23"</font><font color="#007700">;<br />}<br /><br /></font><font color="#FF8000">// this is not necessary...<br /></font><font color="#007700">if (</font><font color="#0000BB">$show_separators </font><font color="#007700">== </font><font color="#0000BB">TRUE</font><font color="#007700">) {<br /> echo </font><font color="#DD0000">"<hr>\n"</font><font color="#007700">;<br />}<br /><br /></font><font color="#FF8000">// ...because you can simply type<br /></font><font color="#007700">if (</font><font color="#0000BB">$show_separators</font><font color="#007700">) {<br /> echo </font><font color="#DD0000">"<hr>\n"</font><font color="#007700">;<br />}<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="language.types.boolean.casting"
>Converting to boolean</A
></H2
><P
> To explicitly convert a value to <A
HREF="language.types.boolean.html"
><B
CLASS="type"
>boolean</B
></A
>, use either
the <VAR
CLASS="literal"
>(bool)</VAR
> or the <VAR
CLASS="literal"
>(boolean)</VAR
> cast.
However, in most cases you do not need to use the cast, since a value
will be automatically converted if an operator, function or
control structure requires a <A
HREF="language.types.boolean.html"
><B
CLASS="type"
>boolean</B
></A
> argument.
</P
><P
> See also <A
HREF="language.types.type-juggling.html"
>Type Juggling</A
>.
</P
><P
> When converting to <A
HREF="language.types.boolean.html"
><B
CLASS="type"
>boolean</B
></A
>, the following values
are considered <TT
CLASS="constant"
><B
>FALSE</B
></TT
>:
<P
></P
><UL
><LI
><P
>the <A
HREF="language.types.boolean.html"
>boolean</A
>
<TT
CLASS="constant"
><B
>FALSE</B
></TT
> itself</P
></LI
><LI
><P
>the <A
HREF="language.types.integer.html"
>integer</A
> 0 (zero) </P
></LI
><LI
><P
>the <A
HREF="language.types.float.html"
>float</A
>
0.0 (zero) </P
></LI
><LI
><P
>the empty <A
HREF="language.types.string.html"
>string</A
>, and the <A
HREF="language.types.string.html"
>string</A
>
"0"</P
></LI
><LI
><P
>an <A
HREF="language.types.array.html"
>array</A
>
with zero elements</P
></LI
><LI
><P
>an <A
HREF="language.types.object.html"
>object</A
>
with zero member variables</P
></LI
><LI
><P
>the special type <A
HREF="language.types.null.html"
>NULL</A
> (including unset variables)
</P
></LI
></UL
>
Every other value is considered <TT
CLASS="constant"
><B
>TRUE</B
></TT
> (including any
<A
HREF="language.types.resource.html"
>resource</A
>).
<DIV
CLASS="warning"
><P
></P
><TABLE
CLASS="warning"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Waarschuwing</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> <VAR
CLASS="literal"
>-1</VAR
> is considered
<TT
CLASS="constant"
><B
>TRUE</B
></TT
>, like any other non-zero (whether negative
or positive) number!
</P
></TD
></TR
></TABLE
></DIV
>
<DIV
CLASS="informalexample"
><P
></P
><A
NAME="AEN2398"
></A
><TABLE
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><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br />var_dump</font><font color="#007700">((bool) </font><font color="#DD0000">""</font><font color="#007700">); </font><font color="#FF8000">// bool(false)<br /></font><font color="#0000BB">var_dump</font><font color="#007700">((bool) </font><font color="#0000BB">1</font><font color="#007700">); </font><font color="#FF8000">// bool(true)<br /></font><font color="#0000BB">var_dump</font><font color="#007700">((bool) -</font><font color="#0000BB">2</font><font color="#007700">); </font><font color="#FF8000">// bool(true)<br /></font><font color="#0000BB">var_dump</font><font color="#007700">((bool) </font><font color="#DD0000">"foo"</font><font color="#007700">); </font><font color="#FF8000">// bool(true)<br /></font><font color="#0000BB">var_dump</font><font color="#007700">((bool) </font><font color="#0000BB">2.3e5</font><font color="#007700">); </font><font color="#FF8000">// bool(true)<br /></font><font color="#0000BB">var_dump</font><font color="#007700">((bool) array(</font><font color="#0000BB">12</font><font color="#007700">)); </font><font color="#FF8000">// bool(true)<br /></font><font color="#0000BB">var_dump</font><font color="#007700">((bool) array()); </font><font color="#FF8000">// bool(false)<br /></font><font color="#0000BB">var_dump</font><font color="#007700">((bool) </font><font color="#DD0000">"false"</font><font color="#007700">); </font><font color="#FF8000">// bool(true)<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
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