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

Programming Errors
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That same statement within the following script is equally wrong:
Except in the possibly rare case in which the variable $var has the value 4, the call to
strstr() will not occur, and no warning will be issued.The PHP interpreter does not
waste time parsing sections of your code that are not needed for the current execution
of the script.You need to be sure that you test carefully!
Calling functions incorrectly is easy to do, but because the resulting error messages
identify the exact line and function call that are causing the problem, they are equally
easy to fix.They are difficult to find only if your testing process is poor and does not test
all conditionally executed code.When you test, one of the goals is to execute every line
of code at least once. Another goal is to test all the boundary conditions and classes of
input.
Reading or Writing Files
Although anything can go wrong at some point during your program’s useful life, some
problems are more likely than others. Because errors accessing files are likely enough to
occur, you need to handle them gracefully. Hard drives fail or fill up, and human error
results in directory permissions changing.
Functions such as fopen() that are likely to fail occasionally generally have a return
value to signal that an error occurred. For fopen(), a return value of false indicates
failure.
For functions that provide failure notification, you need to carefully check the return
value of every call and act on failures.
Interaction with MySQL or Other Databases
Connecting to and using MySQL can generate many errors.The function mysqli_
connect() alone can generate at least the following errors:
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Warning: mysqli_connect() [function.mysqli-connect]: Can’t connect
to MySQL server on ‘localhost’ (10061)
Warning: mysqli_connect() [function.mysqli-connect]: Unknown MySQL
Server Host ‘hostname’ (11001)
Warning: mysqli_connect() [function.mysqli-connect]: Access denied
for user: ‘username’@’localhost’ (Using password: YES)
As you would probably expect, mysqli_connect() provides a return value of false
when an error occurs.This means that you can easily trap and handle these types of
common errors.