ZEND PHP 5 Certification STUDY GUIDE

PHP Basics ” 25
The code above will prevent the call to mysql_connect() from outputting an error—provided
that the function uses PHP’s own functionality for reporting errors.
Sadly, some libraries output their errors directly, bypassing PHP and, therefore, make
it much harder to manage with the error-control operator.
The backtick operator makes it possible to execute a shell command and retrieve
its output. For example, the following will cause the output of the UNIX ls command
to be stored inside $a:
$a = ‘ls -l‘;
i
Don’t confuse the backtick operator with regular quotes (and, conversely, don’t confuse
the latter with the former!)
Operator Precedence and Associativity
As we have all learned in school, not all operations have the same precedence. When
using an infix notation, the order in which operations are written in an expression
lends itself to a certain amount of ambiguity which must, therefore, be resolved. This
can be done in one of two ways: using parentheses to indicate which operations
should be performed first, or by using a set of pre-defined precedence rules.
Even if we establish the precedence of each operation, however, we lack one important
tool: how do we decide in which order we execute operations that have the
same precedence? This is determined by an operation’s associativity, which can either
be left (operations are performed left-to-right), right (operations are performed
right-to-left) or none (for operations that cannot be associated).
The following table illustrates the precedence and associativity of each operation:
Licensed to 482634 - Amber Barrow (itsadmin@deakin.edu.au)