PHP and MySQL for Dynamic Web Sites: Visual QuickPro Guide

PHP Debugging Techniques

Debugging a PHP script—debugging it efficiently, at least—boils down to understanding the normal causes of errors. Table 9.1 lists the likely reasons for the most common PHP errors.

Table 9.1. These are some of the most common errors you’ll see in PHP, along with their most probable causes.

Common PHP Errors
ERROR	LIKELY CAUSE
Parse error	Missing semicolon, unbalanced curly braces, parentheses, or quotation marks, or use of an unescaped quotation mark in a string.
Empty variable value	Forgot the initial $, misspelled or miscapitalized the variable name, inappropriate variable scope, or the register_globals setting is turned off.
Undefined variable	Reference made to a variable before it is given a value.
Call to undefined function ...