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Further explanations on the behaviour of include() and require().

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Also gives differences between PHP3 and PHP4 when using these statements.


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@16743 c90b9560-bf6c-de11-be94-00142212c4b1
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cslawi 1999-12-07 00:02:38 +00:00
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language/control-structures.sgml
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@ -617,22 +617,63 @@ switch ($i):
</sect1>
<sect1 id="function.require">
<title><literal>require</literal></title>
<simpara>
The <literal>require</literal> statement replaces itself with the
specified file, much like the C preprocessor's #include works.</simpara>
<sect1 id="function.require">
<title><function>require</function></title>
<simpara>
The <function>require</function> statement replaces itself with
the specified file, much like the C preprocessor's
<literal>#include</literal> works.
</simpara>
<para>
This means that you can't put a <literal>require</literal>
statement inside of a loop structure and expect it to include the
contents of a different file on each iteration. To do that, use an
<literal>include</literal> statement.
<simpara>
An important note about how this works is that when a file is
<function>include</function>ed or <function>require</function>ed,
parsing drops out of PHP mode and into HTML mode at the beginning
of the target file, and resumes PHP mode again at the end. For
this reason, any code inside the target file which should be
executed as PHP code must be enclosed within <link
linkend="language.basic-syntax.phpmode">valid PHP start and end
tags</link>.
</simpara>
<simpara>
<function>require</function> is not actually a function in PHP;
rather, it is a language construct. It is subject to some
different rules than functions are. For instance,
<function>require</function> is not subject to any containing
control structures. For another, it does not return any value;
attempting to read a return value from a
<function>require</function> call results in a parse error.
</simpara>
<simpara>
Unlike <function>include</function>, <function>require</function>
will <emphasis>always</emphasis> read in the target file,
<emphasis>even if the line it's on never executes</emphasis>. If
you want to conditionally include a file, use
<function>include</function>. The conditional statement won't
affect the <function>require</function>. However, if the line on
which the <function>require</function> occurs is not executed,
neither will any of the code in the target file be executed.
</simpara>
<simpara>
Similarly, looping structures do not affect the behaviour of
<function>require</function>. Although the code contained in the
target file is still subject to the loop, the
<function>require</function> itself happens only once.
</simpara>
<para>
This means that you can't put a <function>require</function>
statement inside of a loop structure and expect it to include the
contents of a different file on each iteration. To do that, use an
<function>include</function> statement.
<informalexample>
<programlisting>
require 'header.inc';
require( 'header.inc' );
</programlisting>
</informalexample>
</para>
@ -648,58 +689,86 @@ switch ($i):
part of the calling file.
<informalexample>
<programlisting>
include( "file.inc?varone=1&amp;vartwo=2" ); /* Won't work. */
require( "file.inc?varone=1&amp;vartwo=2" ); /* Won't work. */
$varone = 1;
$vartwo = 2;
include( "file.inc" ); /* $varone and $vartwo will be available in file.inc */
require( "file.inc" ); /* $varone and $vartwo will be available in file.inc */
</programlisting>
</informalexample>
</para>
<simpara>
Don't be misled by the fact that you can require or include files
via HTTP using the <link linkend="features.remote-files">Remote
files</link> feature; the above holds true regardless.
</simpara>
<simpara>
In PHP3, it is possible to execute a <literal>return</literal>
statement inside a <function>require</function>ed file, as long as
that statement occurs in the global scope of the
<function>require</function>ed file. It may not occur within any
block (meaning inside braces ({}). In PHP4, however, this ability
has been discontinued. If you need this functionality, see
<function>include</function>.
</simpara>
</sect1>
<sect1 id="function.include">
<title><literal>include</literal></title>
<sect1 id="function.include">
<title><function>include</function></title>
<simpara>
The <function>include</function> statement includes and evaluates
the specified file.
</simpara>
<simpara>
The <literal>include</literal> statement includes and evaluates
the specified file.</simpara>
<para>
This happens each time the <literal>include</literal> statement is
encountered, so you can use an <literal>include</literal> statement
within a looping structure to include a number of different file.
<informalexample>
<programlisting>
$files = array ('first.inc', 'second.inc', 'third.inc');
for ($i = 0; $i < count($files); $i++) {
include $files[$i];
}
</programlisting>
</informalexample></para>
<simpara>
An important note about how this works is that when a file is
<function>include</function>ed or <function>require</function>ed,
parsing drops out of PHP mode and into HTML mode at the beginning
of the target file, and resumes again at the end. For this reason,
any code inside the target file which should be executed as PHP
code must be enclosed within <link
linkend="language.basic-syntax.phpmode">valid PHP start and end
tags</link>.
</simpara>
<para>
<link linkend="function.include"><literal>include</literal></link>
differs from <link linkend="function.require"><literal>require</literal></link>
in that the include statement is re-evaluated each time it is
encountered (and only when it is being executed), whereas the
<link linkend="function.require"><literal>require</literal></link>
statement is replaced by the required file when it is first
encountered, whether the contents of the file will be evaluated or
not (for example, if it is inside an if statement whose condition
evaluated to false).</para>
This happens each time the <function>include</function> statement is
encountered, so you can use an <function>include</function> statement
within a looping structure to include a number of different files.
<para>
Because <link linkend="function.include"><literal>include</literal></link> is a
special language construct, you must enclose it within a statement
block if it is inside a conditional block.
<informalexample>
<programlisting>
$files = array ('first.inc', 'second.inc', 'third.inc');
for ($i = 0; $i < count($files); $i++) {
include $files[$i];
}
</programlisting>
</informalexample>
</para>
<para>
<function>include</function> differs from
<function>require</function> in that the include statement is
re-evaluated each time it is encountered (and only when it is
being executed), whereas the <function>require</function>
statement is replaced by the required file when it is first
encountered, whether the contents of the file will be evaluated or
not (for example, if it is inside an <link
linkend="control-structures.if">if</link> statement whose
condition evaluated to false).
</para>
<informalexample>
<programlisting>
<para>
Because <function>include</function> is a special language
construct, you must enclose it within a statement block if it is
inside a conditional block.
<informalexample>
<programlisting>
/* This is WRONG and will not work as desired. */
if ($condition)
@ -714,13 +783,108 @@ include( "file.inc" ); /* $varone and $vartwo will be available in file.inc */
} else {
include($other);
}
</programlisting>
</informalexample></para>
</programlisting>
</informalexample>
</para>
<para>
When the file is evaluated, the parser begins in "HTML-mode" which
will output the contents of the file until the first PHP start tag
(&lt;?) is encountered.</para>
<simpara>
In both PHP3 and PHP4, it is possible to execute a
<literal>return</literal> statement inside an
<function>include</function>ed file, in order to terminate
processing in that file and return to the script which called
it. Some differences in the way this works exist, however. The
first is that in PHP3, the <literal>return</literal> may not
appear inside a block unless it's a function block, in which case
the <literal>return</literal> applies to that function and not the
whole file. In PHP4, however, this restriction does not
exist. Also, PHP4 allows you to return values from
<function>include</function>ed files. You can take the value of the
<function>include</function> call as you would a normal
function. This generates a parse error in PHP3.
</simpara>
<example>
<title><function>include</function> in PHP3 and PHP4</title>
<para>
Assume the existence of the following file (named
<filename>test.inc</filename>) in the same directory as the main
file:
<programlisting>
&lt?php
echo "Before the return &lt;br&gt;\n";
if ( 1 ) {
return 27;
}
echo "After the return &lt;br&gt;\n";
?&gt;
</programlisting>
</para>
<para>
Assume that the main file (<filename>main.html</filename>)
contains the following:
<programlisting>
&lt?php
$retval = include( 'test.inc' );
echo "File returned: '$retval'&lt;br&gt;\n";
?&gt;
</programlisting>
</para>
<para>
When <filename>main.html</filename> is called in PHP3, it will
generate a parse error on line 2; you can't take the value of an
<function>include</function> in PHP3. In PHP4, however, the
result will be:
<screen>
Before the return
File returned: '27'
</screen>
</para>
<para>
Now, assume that <filename>main.html</filename> has been altered
to contain the following:
<programlisting>
&lt?php
include( 'test.inc' );
echo "Back in main.html&lt;br&gt;\n";
?&gt;
</programlisting>
</para>
<para>
In PHP4, the output will be:
<screen>
Before the return
Back in main.html
</screen>
However, PHP3 will give the following output:
<screen>
Before the return
27Back in main.html
Parse error: parse error in /home/torben/public_html/phptest/main.html on line 5
</screen>
</para>
<para>
The above parse error is a result of the fact that the
<literal>return</literal> statement is enclosed in a non-function
block within <filename>test.inc</filename>. When the return is
moved outside of the block, the output is:
<screen>
Before the return
27Back in main.html
</screen>
</para>
<para>
The spurious '27' is due to the fact that PHP3 does not support
<literal>return</literal>ing values from files like that.
</para>
</example>
<para>
Please note that both <function>include</function> and
@ -743,9 +907,17 @@ include( "file.inc" ); /* $varone and $vartwo will be available in file.inc */
</para>
<para>
See also <function>readfile</function>, <function>require</function>,
<function>virtual</function>.</para></sect1>
<simpara>
Don't be misled by the fact that you can require or include files
via HTTP using the <link linkend="features.remote-files">Remote
files</link> feature; the above holds true regardless.
</simpara>
<simpara>
See also <function>readfile</function>,
<function>require</function>, and <function>virtual</function>.
</simpara>
</sect1>
</chapter>