Learning PHP

Chapter 12. Debugging

Programs rarely work correctly the first time you run them. This chapter shows you some techniques for finding and fixing the problems in your programs. When you’re just learning PHP, your programs are probably simpler than the programs that PHP wizards write. The errors you get, however, generally aren’t much simpler, and you have to use the same tools and techniques to find and fix those errors.

Controlling Where Errors Appear

Many things can go wrong in your program that cause the PHP engine to generate an error message. You have a choice about where those error messages go. The messages can be sent along with other program output to the web browser. They can also be included in the web server error log.

A useful way to configure an error message display is to have the errors displayed on screen while you’re developing a PHP program, and then when you’re done with development and people are actually using the program, send error messages to the error log. While you’re working on a program, it’s helpful to see immediately that there was a parse error on a particular line, for example. But once the program is (supposedly) working and your coworkers and customers are using it, such an error message would be confusing to them.

To make error messages display in the browser, set the display_errors configuration directive to On. Set it to Off to prevent error messages from displaying in the browser. To make sure errors end up in the web server error log, keep ...