How to debug a program without a debugger? [closed]

Answer 1

like everyone else said:

• Logging
• Asserts
• Extra Output

&

your favorite task manager or process explorer

links here and here

Answer 2

Peer review. You have been looking at the code for 8 hours and your brain is just showing you what you want to see in the code. A fresh pair of eyes can make all the difference.

Version control. Especially for large teams. If somebody changed something you rely on but did not tell you it is easy to find a specific change set that caused your trouble by rolling the changes back one by one.

Answer 3

Binary search in time is also a method: If you have your source code stored in a version-control repository, and you know that version 100 worked, but version 200 doesn't, try to see if version 150 works. If it does, the error must be between version 150 and 200, so find version 175 and see if it works... etc.

Answer 4

Actually you have quite a lot of possibilities. Either with recompilation of source code or without.

With recompilation.

• Additional logging. Either into program's logs or using system logging (eg. OutputDebugString or Events Log on Windows). Also use following steps:
  • Always include timestamp at least up to seconds resolution.
  • Consider adding thread-id in case of multithreaded apps.
  • Add some nice output of your structures
  • Do not print out enums with just %d. Use some ToString() or create some EnumToString() function (whatever suits your language)
  • ... and beware: logging changes timings so in case of heavily multithreading you problems might disappear.
  • More details on this here.
• Introduce more asserts
• Unit tests
• "Audio-visual" monitoring: if something happens do one of
  • use buzzer
  • play system sound
  • flash some LED by enabling hardware GPIO line (only in embedded scenarios)

Without recompilation

• If your application uses network of any kind: Packet Sniffer or I will just choose for you: Wireshark
• If you use database: monitor queries send to database and database itself.
• Use virtual machines to test exactly the same OS/hardware setup as your system is running on.
• Use some kind of system calls monitor. This includes
  • On Unix box strace or dtrace
  • On Windows tools from former Sysinternals tools like http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx, ProcessExplorer and alike
  • In case of Windows GUI stuff: check out Spy++ or for WPF Snoop (although second I didn't use)
  • Consider using some profiling tools for your platform. It will give you overview on thing happening in your app.
• [Real hardcore] Hardware monitoring: use oscilloscope (aka O-Scope) to monitor signals on hardware lines
• Source code debugging: you sit down with your source code and just pretend with piece of paper and pencil that you are computer. Its so called code analysis or "on-my-eyes" debugging
• Source control debugging. Compare diffs of your code from time when "it" works and now. Bug might be somewhere there.

And some general tips in the end:

• Do not forget about Text to Columns and Pivot Table in Excel. Together with some text tools (awk, grep or perl) give you incredible analysis pack. If you have more than 32K records consider using Access as data source.
• Basics of Data Warehousing might help. With simple cube you may analyse tons of temporal data in just few minutes.
• Dumping your application is worth mentioning. Either as a result of crash or just on regular basis
• Always generate you debug symbols (even for release builds).
• Almost last but not least: most mayor platforms has some sort of command line debugger always built in (even Windows!). With some tricks like conditional debugging and break-print-continue you can get pretty good result with obscure bugs
• And really last but not least: use your brain and question everything.

In general debugging is like science: you do not create it you discover it. Quite often its like looking for a murderer in a criminal case. So buy yourself a hat and never give up.

Answer 5

Spy++ (and more recently Snoop for WPF) are tremendous for getting an insight into Windows UI bugs.

Answer 6

Another thing I have not seen mentioned here that I have had to use quite a bit on embedded systems is serial terminals.

You can cannot a serial terminal to just about any type of device on the planet (I have even done it to embedded CPUs for hydraulics, generators, etc). Then you can write out to the serial port and see everything on the terminal.

You can get real fancy and even setup a thread that listens to the serial terminal and responds to commands. I have done this as well and implemented simple commands to dump a list, see internal variables, etc all from a simple 9600 baud RS-232 serial port!