What is a stacktrace? How do I use a stacktrace to debug my code?

A stacktrace is a list of all the functions and all the files called at a particular point in a piece of code. It may be generated by a programming exception (a runtime error), a break-point, or simply by developer-triggered logging.

If your code crashes, this is useful because it will tell you everywhere that code executed in order to produce the error. Generally, these are good places to start looking for finding a solution to the bug.

Take a look at this PHP error stacktrace...

Stack trace:
#0 /home/anarchocommie/classes/Format/HTML.php(181): users->viewuser()
#1 /home/anarchocommie/classes/Networking/Handler.php(536): HTML->Display()
#2 /home/anarchocommie/classes/Networking/Handler.php(520): Handler->HandleRequest_Content_Format()
#3 /home/anarchocommie/classes/Networking/Handler.php(458): Handler->HandleRequest_Content()
#4 /home/anarchocommie/revoltlib.com/index.php(9): Handler->HandleRequest()
#5 {main}

In this particular stacktrace, index.php was first called (at line 9 in index.php), which then called Handler->HandleRequest(), then Handler->HandleRequest() called Handler->HandleRequest_Content(), and then Handler->HandleRequest_Content() called Handler->HandleRequest_Content_Format(), and then Handler->HandleRequest_Content_Format() called HTML->Display() -- and so on.

Using a stack trace like this, you can find out how and why your errors occurred.