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8.16. Tuning Error Handling

8.16.3. Discussion

Every error generated has an error type associated with it. For example, if you try to array_pop( ) a string, PHP complains that "This argument needs to be an array," since you can only pop arrays. The error type associated with this message is E_NOTICE, a nonfatal runtime problem.

By default, the error reporting level is E_ALL & ~E_NOTICE, which means all error types except notices. The & is a logical AND, and the ~ is a logical NOT. However, the php.ini-recommended configuration file sets the error reporting level to E_ALL, which is all error types.

Error messages flagged as notices are runtime problems that are less serious than warnings. They're not necessarily wrong, but they indicate a potential problem. One example of an E_NOTICE is "Undefined variable," which occurs if you try to use a variable without previously assigning it a value:

// Generates an E_NOTICE
foreach ($array as $value) {
    $html .= $value;
}

// Doesn't generate any error message
$html = '';
foreach ($array as $value) {
    $html .= $value;
}

In the first case, the first time though the foreach, $html is undefined. So, when you append to it, PHP lets you know you're appending to an undefined variable. In the second case, the empty string is assigned to $html above the loop to avoid the E_NOTICE. The previous two code snippets generate identical code because the default value of a variable is the empty string. The E_NOTICE can be helpful because, for example, you may have misspelled a variable name:

foreach ($array as $value) {
    $hmtl .= $value; // oops! that should be $html
}

$html = ''
foreach ($array as $value) {
    $hmtl .= $value; // oops! that should be $html
}

A custom error-handling function can parse errors based on their type and take an appropriate action. A complete list of error types is shown in Table 8-2.

Table 8-2. Error types

Value

Constant

Description

Catchable

1

E_ERROR

Nonrecoverable error

No

2

E_WARNING

Recoverable error

Yes

4

E_PARSE

Parser error

No

8

E_NOTICE

Possible error

Yes

16

E_CORE_ERROR

Like E_ERROR but generated by the PHP core

No

32

E_CORE_WARNING

Like E_WARNING but generated by the PHP core

No

64

E_COMPILE_ERROR

Like E_ERROR but generated by the Zend Engine

No

128

E_COMPILE_WARNING

Like E_WARNING but generated by the Zend Engine

No

256

E_USER_ERROR

Like E_ERROR but triggered by calling trigger_error( )

Yes

512

E_USER_WARNING

Like E_WARNING but triggered by calling trigger_error( )

Yes

1024

E_USER_NOTICE

Like E_NOTICE but triggered by calling trigger_error( )

Yes

2047

E_ALL

Everything

n/a

Errors labeled catchable can be processed by the function registered using set_error_handler( ) . The others indicate such a serious problem that they're not safe to be handled by users, and PHP must take care of them.

8.16.4. See Also

Recipe 8.17 shows how to set up a custom error handler; documentation on error_reporting( ) at http://www.php.net/error-reporting and set_error_handler( ) at http://www.php.net/set-error-handler; for more information about errors, see http://www.php.net/manual/en/ref.errorfunc.php.



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