Cracking the Coding Interview, 4 Edition - 150 Programming Interview Questions and Solutions

Solutions to Chapter 12 | Testing
12.2 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?
SOLUTION
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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.
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