goba Mon Nov 4 05:51:07 2002 EDT
Modified files:
/phpdoc/en/language types.xml
Log:
Adding "Converting to string" section,
which hopefully closes my assigned bug #19575
Done some reorganization in the type juggling
section, added more todo comments
Also added a few examples, in place of some
todo comments
More to come on conversion to other types in the
future...
Index: phpdoc/en/language/types.xml
diff -u phpdoc/en/language/types.xml:1.90 phpdoc/en/language/types.xml:1.91
--- phpdoc/en/language/types.xml:1.90 Sat Oct 26 16:40:41 2002
+++ phpdoc/en/language/types.xml Mon Nov 4 05:51:07 2002
@@ -1,5 +1,5 @@
<?xml version="1.0" encoding="iso-8859-1"?>
-<!-- $Revision: 1.90 $ -->
+<!-- $Revision: 1.91 $ -->
<chapter id="language.types">
<title>Types</title>
@@ -242,7 +242,7 @@
</listitem>
<listitem>
<simpara>an <link linkend="language.types.object">object</link>
- with zero elements</simpara>
+ with zero member variables</simpara>
</listitem>
<listitem>
<simpara>the special type <link linkend="language.types.null"
@@ -393,7 +393,9 @@
the <literal>(int)</literal> or the <literal>(integer)</literal> 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 <type>integer</type> argument.
+ control structure requires an <type>integer</type> argument.
+ You can also convert a value to integer with the function
+ <function>intval</function>.
</simpara>
<simpara>
See also <link linkend="language.types.type-juggling">type-juggling</link>.
@@ -974,8 +976,68 @@
see also the <link linkend="ref.ctype">character type functions</link>.
</simpara>
</sect2>
+ <sect2 id="language.types.string.casting">
+ <title>Converting to string</title>
+
+ <para>
+ You can convert a value to a string using the <literal>(string)</literal>
+ cast, or the <function>strval</function> function. String conversion
+ is automatically done in the scope of an expression for you where a
+ string is needed. This happens when you use the <function>echo</function>
+ or <function>print</function> functions, or when you compare a variable
+ value to a string.
+ </para>
+
+ <para>
+ A boolean &true; value is converted to the string <literal>"1"</literal>,
+ the &false; value is represented as <literal>""/literal> (empty string).
+ This way you can convert back and forth between boolean and string values.
+ </para>
+ <para>
+ An integer or a floating point number is converted to a string
+ representing the number with its digits (includig the exponent part
+ for floating point numbers).
+ </para>
+ <para>
+ Arrays are always converted to the string <literal>"Array"</literal>,
+ so you cannot dump out the contents of an array with <function>echo</function>
+ or <function>print</function> to see what is inside them. See the information
+ below for more tips.
+ </para>
+ <para>
+ Objects are always converted to the string <literal>"Object"</literal>.
+ If you would like to print out the member variable values of an object
+ for debugging reasons, read the paragraphs below. If you would
+ like to find out the class name of which an object is an instance of,
+ use <function>get_class</function>.
+ </para>
+ <para>
+ Resources are always converted to strings with the structure
+ <literal>"Resource id #1"</literal> where <literal>1</literal> is
+ the unique number of the resource assigned by PHP during runtime.
+ </para>
+ <para>
+ &null; is always converted to an empty string.
+ </para>
+
+ <para>
+ As you can see above, printing out the arrays, objects or resources does not
+ provide you any useful information about the values themselfs. Look at the
+ functions <function>print_r</function> and <function>var_dump</function>
+ for better ways to print out values for debugging.
+ </para>
+
+ <para>
+ You can also convert PHP values to strings to store them permanently. This
+ method is called serialization, and can be done with the function
+ <function>serialize</function>. You can also serialize PHP values to
+ XML structures, if you have <link linkend="ref.wddx">WDDX</link> support
+ in your PHP setup.
+ </para>
+ </sect2>
+
<sect2 id="language.types.string.conversion">
- <title>String conversion</title>
+ <title>String conversion to numbers</title>
<simpara>
When a string is evaluated as a numeric value, the resulting
@@ -1937,9 +1999,9 @@
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 <parameter>var</parameter>,
- <parameter>var</parameter> becomes a string. If you then assign an
- integer value to <parameter>var</parameter>, it becomes an
+ assign a string value to variable <parameter>$var</parameter>,
+ <parameter>$var</parameter> becomes a string. If you then assign an
+ integer value to <parameter>$var</parameter>, it becomes an
integer.
</simpara>
<para>
@@ -1984,7 +2046,7 @@
<simpara>
If the last two examples above seem odd, see <link
linkend="language.types.string.conversion">String
- conversion</link>.
+ conversion to numbers</link>.
</simpara>
<simpara>
If you wish to force a variable to be evaluated as a certain type,
@@ -2010,15 +2072,27 @@
</informalexample>
</para>
<para>
- Since PHP 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?
+ 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?
</para>
<para>
- For this reason, as of PHP 3.0.12 and PHP 4.0b3-RC4, the result
- of this automatic conversion is considered to be undefined. Fixes
- are, however, being discussed.
+ The current versions of PHP interpret the second assignment as
+ a string offset identification, so $a becomes "f", the result
+ of this automatic conversion however should be considered
+ undefined. PHP 4 introduced the new curly bracket syntax to access
+ characters in string, use this syntax instead of the one presented
+ above:
+ <informalexample>
+ <programlisting role="php">
+$a = "abc"; // $a is a string
+$a{1} = "f"; // $a is now "afc"
+ </programlisting>
+ </informalexample>
+ See the section titled <link linkend="language.types.string.substr">String
+ access by character</link> for more informaton.
</para>
</note>
@@ -2032,7 +2106,7 @@
<informalexample>
<programlisting role="php">
$foo = 10; // $foo is an integer
-$bar = (float) $foo; // $bar is a float
+$bar = (boolean) $foo; // $bar is a boolean
</programlisting>
</informalexample>
</para>
@@ -2059,14 +2133,6 @@
</listitem>
</itemizedlist>
</para>
- <note>
- <simpara>
- Instead of casting a variable to string, you can also enclose
- the variable in double quotes.
- <!-- TODO: example -->
- </simpara>
- </note>
-
<para>
Note that tabs and spaces are allowed inside the parentheses, so
the following are functionally equivalent:
@@ -2077,6 +2143,25 @@
</programlisting>
</informalexample>
</para>
+ <note>
+ <simpara>
+ Instead of casting a variable to string, you can also enclose
+ the variable in double quotes.
+ <informalexample>
+ <programlisting role="php">
+$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";
+}
+ </programlisting>
+ </informalexample>
+ </simpara>
+ </note>
+
<para>
It may not be obvious exactly what will happen when casting
between certain types. For more info, see these sections:
@@ -2090,16 +2175,16 @@
<simpara><link linkend="language.types.integer.casting">Converting to
integer</link></simpara>
</listitem>
+ <listitem>
+ <simpara><link linkend="language.types.string.casting">Converting to
+ string</link></simpara>
+ </listitem>
<!-- don't exist yet
<listitem>
<simpara><link linkend="language.types.float.casting">Converting to
float</link></simpara>
</listitem>
<listitem>
- <simpara><link linkend="language.types.string.casting">Converting to
- string</link></simpara>
- </listitem>
- <listitem>
<simpara><link linkend="language.types.array.casting">Converting to
array</link></simpara>
</listitem>
@@ -2120,19 +2205,7 @@
</para>
<para>
- <!-- TODO: move to 'converting to string' -->
- When casting or forcing a conversion from array to string, the
- result will be the word <literal>Array</literal>. When casting or
- forcing a conversion from object to string, the result will be
- the word <literal>Object</literal>.
-
- <!-- not with my PHP, not even a notice... maybe in PHP3?
- Does someone know?
-
- In both cases a warning will
- be issued. -->
- </para>
- <para>
+ <!-- TODO: move to 'converting to array' -->
When casting from a scalar or a string variable to an array, the
variable will become the first element of the array:
<informalexample>
@@ -2144,6 +2217,7 @@
</informalexample>
</para>
<para>
+ <!-- TODO: move to 'converting to object' -->
When casting from a scalar or a string variable to an object, the
variable will become an attribute of the object; the attribute
name will be 'scalar':
--
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