There are several types of errors and warnings in PHP. They are:
Table 15-1. PHP error types
|1||E_ERROR||fatal run-time errors|
|2||E_WARNING||run-time warnings (non fatal errors)|
|4||E_PARSE||compile-time parse errors|
|8||E_NOTICE||run-time notices (less serious than warnings)|
|16||E_CORE_ERROR||fatal errors that occur during PHP's initial startup||PHP 4 only|
|32||E_CORE_WARNING||warnings (non fatal errors) that occur during PHP's initial startup||PHP 4 only|
|64||E_COMPILE_ERROR||fatal compile-time errors||PHP 4 only|
|128||E_COMPILE_WARNING||compile-time warnings (non fatal errors)||PHP 4 only|
|256||E_USER_ERROR||user-generated error message||PHP 4 only|
|512||E_USER_WARNING||user-generated warning message||PHP 4 only|
|1024||E_USER_NOTICE||user-generated notice message||PHP 4 only|
|E_ALL||all of the above, as supported|
The above values (either numerical or symbolic) are used to build up a bitmask that specifies which errors to report. You can use the bitwise operators to combine these values or mask out certain types of errors. Note that only '|', '~', '!', and '&' will be understood within php.ini, however, and that no bitwise operators will be understood within php3.ini.
In PHP 4, the default error_reporting setting is E_ALL & ~E_NOTICE, meaning to display all errors and warnings which are not E_NOTICE-level. In PHP 3, the default setting is (E_ERROR | E_WARNING | E_PARSE), meaning the same thing. Note, however, that since constants are not supported in PHP 3's php3.ini, the error_reporting setting there must be numeric; hence, it is 7.
The initial setting can be changed in the ini file with the error_reporting directive, in your Apache httpd.conf file with the php_error_reporting (php3_error_reporting for PHP 3) directive, and lastly it may be set at runtime within a script by using the error_reporting() function.
When upgrading code or servers from PHP 3 to PHP 4 you should check these settings and calls to error_reporting() or you might disable reporting the new error types, especially E_COMPILE_ERROR. This may lead to empty documents without any feedback of what happened or where to look for the problem.
All PHP expressions can also be called with the "@" prefix, which turns off error reporting for that particular expression. If an error occurred during such an expression and the track_errors feature is enabled, you can find the error message in the global variable $php_errormsg.
Currently the @ error-control operator prefix will even disable error reporting for critical errors that will terminate script execution. Among other things, this means that if you use @ to suppress errors from a certain function and either it isn't available or has been mistyped, the script will die right there with no indication as to why.
Below we can see an example of using the error handling capabilities in PHP. We define a error handling function which logs the information into a file (using an XML format), and e-mails the developer in case a critical error in the logic happens.
Example 15-1. Using error handling in a script