PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Handling Errors Gracefully
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You use trigger_error() as follows:
trigger_error('This computer will self destruct in 15 seconds', E_USER_WARNING);
Handling Errors Gracefully
If you come from a C++ or Java background, you are probably comfortable using
exceptions. Exceptions allow functions to signal that an error has occurred and leave
dealing with the error to an exception handler. Exceptions are an excellent way to handle
errors in large projects.They were adequately covered in Chapter 7,“Error and
Exception Handling,” so they will not be revisited here.
You have already seen how you can trigger your own errors.You can also provide
your own error handlers to catch errors.
The function set_error_handler() lets you provide a function to be called when
user-level errors, warnings, and notices occur.You call set_error_handler() with the
name of the function you want to use as your error handler.
Your error handling function must take two parameters: an error type and an error
message. Based on these two variables, your function can decide how to handle the
error.The error type must be one of the defined error type constants.The error message
is a descriptive string.
A call to set_error_handler() looks like this:
set_error_handler('my_error_handler');
Having told PHP to use a function called my_error_handler(), you must then provide
a function with that name.This function must have the following prototype:
My_error_handler(int error_type, string error_msg
[, string errfile [, int errline [, array errcontext]]]))
What it actually does, however, is up to you.
The parameters passed to your handler function are
n The error type
n The error message
n The file the error occurred in
n The line the error occurred on
n The symbol table—that is, a set of all the variables and their values at the time the
error occurred
Logical actions might include
n Displaying the error message provided
n Storing information in a log file
n Emailing the error to an address
n Terminating the script with a call to exit