Core PHP Programming: Using PHP to Build Dynamic Web Sites

In-Line Debugging

There are times when code produces unexpected results. Examining the code reveals nothing. In this case the best thing to do is some in-line debugging. PHP scripts generate HTML to be interpreted by a browser, and HTML has a comment tag. Therefore, it is a simple matter to write PHP code that reports diagnostic information inside HTML comments.

Often I create database queries dynamically, based on user input. A stray character or invalid user input can cause the query to return an error. Sometimes I will print the query itself. I also print the results of the error functions, such as mysql_error. The same applies to code unrelated to databases. Printing diagnostic information, even if it is as simple as saying "got here," can ...