Learning PHP 5

Chapter 12. Debugging

Programs rarely work correctly the first time. 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 interpreter 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 when you’re developing a PHP program, and then sent to the error log once you’re done development and people are actually using the program. 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 so that your coworkers or customers can use 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. To send errors to the web server error log, set log_errors to On. You can set them both to On if you want error messages in both places.

An error message that the ...