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>Type Juggling</TITLE
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>Chapter 7. Types</TD
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><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="language.types.type-juggling"
></A
>Type Juggling</H1
><P
>&#13;    PHP does not require (or support) explicit type definition in
    variable declaration; a variable's type is determined by the
    context in which that variable is used. That is to say, if you
    assign a string value to variable <TT
CLASS="parameter"
><I
>$var</I
></TT
>,
    <TT
CLASS="parameter"
><I
>$var</I
></TT
> becomes a string. If you then assign an
    integer value to <TT
CLASS="parameter"
><I
>$var</I
></TT
>, it becomes an
    integer.
   </P
><P
>&#13;    An example of PHP's automatic type conversion is the addition
    operator '+'. If any of the operands is a float, then all
    operands are evaluated as floats, and the result will be a
    float. Otherwise, the operands will be interpreted as integers,
    and the result will also be an integer. Note that this does NOT
    change the types of the operands themselves; the only change is in
    how the operands are evaluated.
    <DIV
CLASS="informalexample"
><A
NAME="AEN3895"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>&#60;?php
$foo = "0";  // $foo is string (ASCII 48)
&#60;!-- bad example, no real operator (must be used with variable, modifies it too)
$foo++;      // $foo is the string "1" (ASCII 49)
--&#62;
$foo += 2;   // $foo is now an integer (2)
$foo = $foo + 1.3;  // $foo is now a float (3.3)
$foo = 5 + "10 Little Piggies"; // $foo is integer (15)
$foo = 5 + "10 Small Pigs";     // $foo is integer (15)
&#60;!--

TODO: explain ++/- - behaviour with strings

examples:

++'001' = '002'
++'abc' = 'abd'
++'xyz' = 'xza'
++'9.9' = '9.0'
++'-3'  = '-4'
- -'9'   = 8 (integer!)
- -'5.5' = '5.5'
- -'-9'  = -10 (integer)
- -'09'  = 8 (integer)
- -'abc' = 'abc'

--&#62;
?&#62;</PRE
></TD
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><P
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></DIV
>
   </P
><P
>&#13;    If the last two examples above seem odd, see <A
HREF="language.types.string.html#language.types.string.conversion"
>String
    conversion to numbers</A
>.
   </P
><P
>&#13;    If you wish to force a variable to be evaluated as a certain type,
    see the section on <A
HREF="language.types.type-juggling.html#language.types.typecasting"
>Type
    casting</A
>. If you wish to change the type of a variable, see
    <A
HREF="function.settype.html"
><B
CLASS="function"
>settype()</B
></A
>.
   </P
><P
>&#13;    If you would like to test any of the examples in this section, you
    can use the <A
HREF="function.var-dump.html"
><B
CLASS="function"
>var_dump()</B
></A
> function.
   </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
     The behaviour of an automatic conversion to array is currently
     undefined.
    </P
><P
>&#13;     <DIV
CLASS="informalexample"
><A
NAME="AEN3907"
></A
><P
></P
><TABLE
BORDER="0"
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CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>&#60;?php
$a = "1";     // $a is a string
$a[0] = "f";  // What about string offsets? What happens?
?&#62;</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
    </P
><P
>&#13;     Since PHP (for historical reasons) supports indexing into strings
     via offsets using the same syntax as array indexing, the example
     above leads to a problem: should $a become an array with its first
     element being "f", or should "f" become the first character of the
     string $a?
    </P
><P
>&#13;     The current versions of PHP interpret the second assignment as
     a string offset identification, so $a becomes "f", the result
     of this automatic conversion however should be considered
     undefined. PHP 4 introduced the new curly bracket syntax to access
     characters in string, use this syntax instead of the one presented
     above: 
     <DIV
CLASS="informalexample"
><A
NAME="AEN3911"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>&#60;?php
$a    = "abc"; // $a is a string
$a{1} = "f";   // $a is now "afc"
?&#62;</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
     See the section titled <A
HREF="language.types.string.html#language.types.string.substr"
>String
     access by character</A
> for more informaton.
    </P
></BLOCKQUOTE
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="language.types.typecasting"
></A
>Type Casting</H2
><P
>&#13;     Type casting in PHP works much as it does in C: the name of the
     desired type is written in parentheses before the variable which
     is to be cast.
     <DIV
CLASS="informalexample"
><A
NAME="AEN3917"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>&#60;?php
$foo = 10;   // $foo is an integer
$bar = (boolean) $foo;   // $bar is a boolean
?&#62;</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
    </P
><P
>&#13;     The casts allowed are:
     <P
></P
><UL
><LI
><P
>(int), (integer) - cast to integer</P
></LI
><LI
><P
>(bool), (boolean) - cast to boolean</P
></LI
><LI
><P
>(float), (double), (real) - cast to float</P
></LI
><LI
><P
>(string) - cast to string</P
></LI
><LI
><P
>(array) - cast to array</P
></LI
><LI
><P
>(object) - cast to object</P
></LI
></UL
>
    </P
><P
>&#13;     Note that tabs and spaces are allowed inside the parentheses, so
     the following are functionally equivalent:
     <DIV
CLASS="informalexample"
><A
NAME="AEN3934"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>&#60;?php
$foo = (int) $bar;
$foo = ( int ) $bar;
?&#62;</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
    </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
      Instead of casting a variable to string, you can also enclose
      the variable in double quotes.
     <DIV
CLASS="informalexample"
><A
NAME="AEN3938"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>&#60;?php
$foo = 10;            // $foo is an integer
$str = "$foo";        // $str is a string
$fst = (string) $foo; // $fst is also a string

// This prints out that "they are the same"
if ($fst === $str) {
    echo "they are the same";
}
?&#62;</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
     </P
></BLOCKQUOTE
></DIV
><P
>&#13;     It may not be obvious exactly what will happen when casting
     between certain types. For more info, see these sections:
    
     <P
></P
><UL
><LI
><P
><A
HREF="language.types.boolean.html#language.types.boolean.casting"
>Converting to 
        boolean</A
></P
></LI
><LI
><P
><A
HREF="language.types.integer.html#language.types.integer.casting"
>Converting to 
        integer</A
></P
></LI
><LI
><P
><A
HREF="language.types.float.html#language.types.float.casting"
>Converting to 
        float</A
></P
></LI
><LI
><P
><A
HREF="language.types.string.html#language.types.string.casting"
>Converting to 
        string</A
></P
></LI
><LI
><P
><A
HREF="language.types.array.html#language.types.array.casting"
>Converting to 
        array</A
></P
></LI
><LI
><P
><A
HREF="language.types.object.html#language.types.object.casting"
>Converting to 
        object</A
></P
></LI
><LI
><P
><A
HREF="language.types.resource.html#language.types.resource.casting"
>Converting to 
        resource</A
></P
></LI
></UL
>
    </P
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