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PEAR

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PEAR -- PEAR base class

Synopsis

require_once "PEAR.php";
class classname extends PEAR { ... }

Description

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.

Its key features are:

PEAR "destructors"

If you inherit PEAR in a class called ClassName, you can define a method in it called called _ClassName (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 the example below.

PEAR Error Handling

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 PEAR_Error, or some class inheriting PEAR_Error.

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).

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 trigger_error() function, invoke a callback, or none of the above. This is typically specified in PEAR_Error's constructor, but all of the parameters are optional, and you can set up defaults for errors generated from each object based on the PEAR class. See the PEAR error examples for how to use it and the PEAR_Error reference for the full details.

Examples

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 1. PEAR: emulated destructors


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.

Note: PEAR "destructors" use PHP's shutdown callbacks (register_shutdown_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.

The next examples illustrate different ways of using PEAR's error handling mechanism.

Example 2. PEAR error example (1)


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()."<BR>\n"
}

This example shows a wrapper to fsockopen() that delivers the error code and message (if any) returned by fsockopen in a PEAR error object. Notice that PEAR::isError() is used to detect whether a value is a PEAR error.

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.

In the next example we're showing how to use default error modes:

Example 3. PEAR error example (2)


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<BR>\n";

Here, we set the default error mode to PEAR_ERROR_DIE, 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.

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