Chapter 3

Debugging PHP Code


Bullet Setting up PHP for debugging

Bullet Examining the PHP error log

Bullet Outputting variable values with echo and print

Bullet Making good use of print_r()

Bullet Getting to know var_dump()

The most effective debugging tool is still careful thought, coupled with judiciously placed print statements.


Debugging — the art, science, and (sometimes) magic of finding and correcting programming errors — is a vital part of all web development. Why? Because no one — not even the nerdiest and most experienced of coders — can write anything moderately complex without introducing an error (or, more likely, a half dozen errors). Programming just works that way. Don’t ask me why because I really have no idea. It just does. So, when some code doesn’t work the first time (or even the tenth time), it doesn’t mean you’re a lousy coder. It just means you’re normal. Believe me, it happens to absolutely everyone who codes.

JavaScript code runs inside the browser, so debugging ...

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