php-doc-en/pear/pear.xml
2001-07-07 21:27:21 +00:00

383 lines
12 KiB
XML

<reference id="ref.pear">
<title>PEAR Reference Manual</title>
<titleabbrev>PEAR</titleabbrev>
<partintro>
<simpara>
This chapter contains reference documentation for PEAR components
that are distributed with PHP. It is assumed that you are
already familiar with <link linkend="language.oop">objects and
classes</link>.
</simpara>
</partintro>
<refentry id="class.pear">
<refnamediv>
<refname>PEAR</refname>
<refpurpose>PEAR base class</refpurpose>
</refnamediv>
<refsynopsisdiv>
<synopsis>require_once "PEAR.php";</synopsis>
<synopsis>class <replaceable>classname</replaceable> extends <classname>PEAR</classname> { ... }</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<simpara>
The PEAR base class provides standard functionality that is used
by most PEAR classes. Normally you never make an instance of the
PEAR class directly, you use it by subclassing it.
</simpara>
<para>
Its key features are:
<itemizedlist>
<listitem>
<simpara>request-shutdown object "destructors"</simpara>
</listitem>
<listitem>
<simpara>error handling</simpara>
</listitem>
</itemizedlist>
</para>
<refsect2>
<title>PEAR "destructors"</title>
<simpara>
If you inherit <classname>PEAR</classname> in a class called
<replaceable>ClassName</replaceable>, you can define a method in
it called called _<replaceable>ClassName</replaceable> (the
class name with an underscore prepended) that will be invoked
when the request is over. This is not a destructor in the sense
that you can "delete" an object and have the destructor called,
but in the sense that PHP gives you a callback in the object
when it is done executing. See <link
linkend="example.pear.destructors">the example</link> below.
</simpara>
</refsect2>
<refsect2>
<title>PEAR Error Handling</title>
<simpara>
PEAR's base class also provides a way of passing around more
complex errors than a &true;/false value or a numeric code. A
PEAR error is an object that is either an instance of the class
<classname>PEAR_Error</classname>, or some class inheriting
<classname>PEAR_Error</classname>.
</simpara>
<simpara>
One of the design criteria of PEAR's errors is that it should
not force a particular type of output on the user, it should be
possible to handle errors without any output at all if that is
desireable. This makes it possible to handle errors gracefully,
also when your output format is different from HTML (for example
WML or some other XML format).
</simpara>
<simpara>
The error object can be configured to do a number of things when
it is created, such as printing an error message, printing the
message and exiting, raising an error with PHP's
<function>trigger_error</function> function, invoke a callback,
or none of the above. This is typically specified in
<classname>PEAR_Error</classname>'s constructor, but all of the
parameters are optional, and you can set up defaults for errors
generated from each object based on the
<classname>PEAR</classname> class. See the <link
linkend="example.pear.error1">PEAR error examples</link> for how
to use it and the <classname>PEAR_Error</classname> reference
for the full details.
</simpara>
</refsect2>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
The example below shows how to use the PEAR's "poor man's kinda
emulated destructors" to implement a simple class that holds the
contents of a file, lets you append data to the object and
flushes the data back to the file at the end of the request:
<example id="example.pear.destructors">
<title>PEAR: emulated destructors</title>
<programlisting role="php">
require_once "PEAR.php";
class FileContainer extends PEAR
{
var $file = '';
var $contents = '';
var $modified = 0;
function FileContainer($file)
{
$this->PEAR(); // this calls the parent class constructor
$fp = fopen($file, "r");
if (!is_resource($fp)) {
return;
}
while (!empty($data = fread($fp, 2048))) {
$this->contents .= $data;
}
fclose($fp);
}
function append($str)
{
$this->contents .= $str;
$this->modified++;
}
// The "destructor" is named like the constructor
// but with an underscore in front.
function _FileContainer()
{
if ($this->modified) {
$fp = fopen($this->file, "w");
if (!is_resource($fp)) {
return;
}
fwrite($fp, $this->contents);
fclose($fp);
}
}
}
$fileobj = new FileContainer("testfile");
$fileobj->append("this ends up at the end of the file\n");
// When the request is done and PHP shuts down, $fileobj's
// "destructor" is called and updates the file on disk.
</programlisting>
</example>
<note>
<simpara>
PEAR "destructors" use PHP's shutdown callbacks
(<function>register_shutdown_function</function>), and you
can't output anything from these when PHP is running in a web
server. So anything printed in a "destructor" gets lost except
when PHP is used in command-line mode. Bummer.
</simpara>
</note>
</para>
<simpara>
The next examples illustrate different ways of using PEAR's error
handling mechanism.
</simpara>
<para>
<example id="example.pear.error1">
<title>PEAR error example (1)</title>
<programlisting role="php">
function mysockopen($host = "localhost", $port = 8090)
{
$fp = fsockopen($host, $port, $errno, $errstr);
if (!is_resource($fp)) {
return new PEAR_Error($errstr, $errno);
}
return $fp;
}
$sock = mysockopen();
if (PEAR::isError($sock)) {
print "mysockopen error: ".$sock->getMessage()."&lt;BR>\n"
}
</programlisting>
</example>
</para>
<simpara>
This example shows a wrapper to <function>fsockopen</function>
that delivers the error code and message (if any) returned by
fsockopen in a PEAR error object. Notice that
<function>PEAR::isError</function> is used to detect whether a
value is a PEAR error.
</simpara>
<simpara>
PEAR_Error's mode of operation in this example is simply
returning the error object and leaving the rest to the user
(programmer). This is the default error mode.
</simpara>
<simpara>
In the next example we're showing how to use default error modes:
</simpara>
<para>
<example id="example.pear.error2">
<title>PEAR error example (2)</title>
<programlisting role="php">
class TCP_Socket extends PEAR
{
var $sock;
function TCP_Socket()
{
$this->PEAR();
}
function connect($host, $port)
{
$sock = fsockopen($host, $port, $errno, $errstr);
if (!is_resource($sock)) {
return $this->raiseError($errstr, $errno);
}
}
}
$sock = new TCP_Socket;
$sock->setErrorHandling(PEAR_ERROR_DIE);
$sock->connect("localhost", 8090);
print "still alive&lt;BR>\n";
</programlisting>
</example>
</para>
<simpara>
Here, we set the default error mode to
<constant>PEAR_ERROR_DIE</constant>, and since we don't specify
any error mode in the raiseError call (that'd be the third
parameter), raiseError uses the default error mode and exits if
fsockopen fails.
</simpara>
</refsect1>
</refentry>
<refentry id="class.pear-error">
<refnamediv>
<refname>PEAR_Error</refname>
<refpurpose>PEAR error mechanism base class</refpurpose>
</refnamediv>
<refsynopsisdiv>
<synopsis>$err = new <classname>PEAR_Error</classname>($msg);</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Error Modes</title>
<para>
An error object has a mode of operation that can be set with one
of the following constants:
<variablelist id="pear.error-modes">
<varlistentry id="constant.pear-error-return">
<term>PEAR_ERROR_RETURN</term>
<listitem>
<simpara>
Just return the object, don't do anything special in
PEAR_Error's constructor.
</simpara>
</listitem>
</varlistentry>
<varlistentry id="constant.pear-error-print">
<term>PEAR_ERROR_PRINT</term>
<listitem>
<simpara>
Print the error message in the constructor. The execution is
not interrupted.
</simpara>
</listitem>
</varlistentry>
<varlistentry id="constant.pear-error-trigger">
<term>PEAR_ERROR_TRIGGER</term>
<listitem>
<simpara>
Use PHP's <function>trigger_error</function> function to
raise an internal error in PHP. The execution is aborted if
you have defined your own PHP error handler or if you set the
error severity to E_USER_ERROR.
</simpara>
</listitem>
</varlistentry>
<varlistentry id="constant.pear-error-die">
<term>PEAR_ERROR_DIE</term>
<listitem>
<simpara>
Print the error message and exit. Execution is of course
aborted.
</simpara>
</listitem>
</varlistentry>
<varlistentry id="constant.pear-error-callback">
<term>PEAR_ERROR_CALLBACK</term>
<listitem>
<simpara>
Use a callback function or method to handle errors.
Execution is aborted.
</simpara>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1>
<title>Properties</title>
<simpara></simpara>
</refsect1>
<refsect1>
<title>Methods</title>
<funcsynopsis>
<funcprototype>
<funcdef><function>PEAR_Error::PEAR_Error</function></funcdef>
<paramdef>
<parameter><optional>message</optional></parameter>
<parameter><optional>code</optional></parameter>
<parameter><optional>mode</optional></parameter>
<parameter><optional>options</optional></parameter>
<parameter><optional>userinfo</optional></parameter>
</paramdef>
</funcprototype>
</funcsynopsis>
<refsect2>
<title>Description</title>
<para>
PEAR_Error constructor. Parameters:
<variablelist>
<varlistentry>
<term>message</term>
<listitem>
<simpara>
error message, defaults to "unknown error"
</simpara>
</listitem>
</varlistentry>
<varlistentry>
<term>code</term>
<listitem>
<simpara>
error code (optional)
</simpara>
</listitem>
</varlistentry>
<varlistentry>
<term>mode</term>
<listitem>
<simpara>
Mode of operation. See the <link
linkend="pear.error-modes">error modes</link> section for
details.
</simpara>
</listitem>
</varlistentry>
<varlistentry>
<term>options</term>
<listitem>
<simpara>
If the mode of can have any options specified, use this
parameter. Currently the "trigger" and "callback" modes are
the only using the options parameter. For trigger mode,
this parameter is one of <constant>E_USER_NOTICE</constant>,
<constant>E_USER_WARNING</constant> or
<constant>E_USER_ERROR</constant>. For callback mode, this
parameter should contain either the callback function name
(string), or a two-element (object, string) array
representing an object and a method name.
</simpara>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
</refsect1>
</refentry>
</reference>
<!-- 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
sgml-parent-document:nil
sgml-default-dtd-file:"../../manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
-->