Programming errors cause program crashes in different places every single time

You are given the source to an application which crashes when it is run. After running it ten times in a debugger, you find it never crashes in the same place. The application is single threaded, and uses only the C standard library. What programming errors could be causing this crash? How would you test each one?

My initial thoughts:
There are only two possible reasons that I can think of:

  1. The program involves with random number generation and it causes some error afterward.
  2. Some variables are not initialized hence causing further crashes.

The question largely depends on the type of application being diagnosed. However, we can give some general causes of random crashes.

  1. Random variable: The application uses some random number or variable component which may not be fixed for every execution of the program. Examples include: user input, a random number generated by the program, or the time of day.
  2. Memory Leak: The program may have run out of memory. Other culprits are totally random for each run since it depends on the number of processes running at that particular time. This also includes heap overflow or corruption of data on the stack.

It is also possible that the program depends on another application / external module that could lead to the crash. If our application, for example, depends on some system attributes and they are modified by another program, then this interference may lead to a crash. Programs which interact with hardware are more prone to these errors.
In an interview, we should ask about which kind of application is being run. This information may give you some idea about the kind of error the interviewer is looking for. For example, a web server is more prone to memory leakage, whereas a program that runs close to the system level is more prone to crashes due to system dependencies.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: