Bugs!

Your bug reports play an essential role in making Octave reliable.

When you encounter a problem, the first thing to do is to see if it is already known. Octave's manual contains a list of known causes of trouble. Another place to look to see if your problem has been reported (and perhaps already solved) is the archive of bug repots for Octave. If you your problem does not appear to be known, then you should report the problem.

Reporting a bug may help you by bringing a solution to your problem, or it may not. In any case, the principal function of a bug report is to help the entire community by making the next version of Octave work better. Bug reports are your contribution to the maintenance of Octave.

In order for a bug report to serve its purpose, you must include the information that makes it possible to fix the bug.

Have You Found a Bug?

If you are not sure whether you have found a bug, here are some guidelines:

• If Octave gets a fatal signal, for any input whatever, that is a bug. Reliable interpreters never crash.
• If Octave produces incorrect results, for any input whatever, that is a bug.
• Some output may appear to be incorrect when it is in fact due to a program whose behavior is undefined, which happened by chance to give the desired results on another system. For example, the range operator may produce different results because of differences in the way floating point arithmetic is handled on various systems.
• If Octave produces an error message for valid input, that is a bug.
• If Octave does not produce an error message for invalid input, that is a bug. However, you should note that your idea of "invalid input" might be my idea of "an extension" or "support for traditional practice".
• If you are an experienced user of programs like Octave, your suggestions for improvement are welcome in any case.

Where and How to Send Bug Reports

If you have Octave working at all, the easiest way to prepare a complete bug report is to use the Octave function bug_report. When you execute this function, Octave will prompt you for a subject and then invoke the editor on a file that already contains all the configuration information. When you exit the editor, Octave will mail the bug report for you.

Please do not send bug reports to the help-octave mailing list. Most users of Octave do not want to receive bug reports. Those that do have asked to be on the bug-octave mailing list.

Making Your Bug Report Count

The fundamental principle of reporting bugs usefully is this: report all the facts. If you are not sure whether to state a fact or leave it out, state it!

Often people omit facts because they think they know what causes the problem and they conclude that some details don't matter. Thus, you might assume that the name of the variable you use in an example does not matter. Well, probably it doesn't, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the interpreter into doing the right thing despite the bug. Play it safe and give a specific, complete example.

Keep in mind that the purpose of a bug report is to enable someone to fix the bug if it is not known. Always write your bug reports on the assumption that the bug is not known.

Sometimes people give a few sketchy facts and ask, "Does this ring a bell?" This cannot help us fix a bug. It is better to send a complete bug report to begin with.

Try to make your bug report self-contained. If we have to ask you for more information, it is best if you include all the previous information in your response, as well as the information that was missing.

To enable someone to investigate the bug, you should include all these things:

• The version of Octave. You can get this by noting the version number that is printed when Octave starts, or running it with the -v option.
• A complete input file that will reproduce the bug. A single statement may not be enough of an example--the bug might depend on other details that are missing from the single statement where the error finally occurs.
• The command arguments you gave Octave to execute that example and observe the bug. To guarantee you won't omit something important, list all the options. If we were to try to guess the arguments, we would probably guess wrong and then we would not encounter the bug.
• The type of machine you are using, and the operating system name and version number.
• The command-line arguments you gave to the configure command when you installed the interpreter.
• A complete list of any modifications you have made to the interpreter source. Be precise about these changes--show a context diff for them.
• Details of any other deviations from the standard procedure for installing Octave.
• A description of what behavior you observe that you believe is incorrect. For example, "The interpreter gets a fatal signal," or, "The output produced at line 208 is incorrect." Of course, if the bug is that the interpreter gets a fatal signal, then one can't miss it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong. Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of the interpreter is out of synch, or you have encountered a bug in the C library on your system. Your copy might crash and the copy here would not. If you said to expect a crash, then when the interpreter here fails to crash, we would know that the bug was not happening. If you don't say to expect a crash, then we would not know whether the bug was happening. We would not be able to draw any conclusion from our observations. Often the observed symptom is incorrect output when your program is run. Unfortunately, this is not enough information unless the program is short and simple. It is very helpful if you can include an explanation of the expected output, and why the actual output is incorrect.
• If you wish to suggest changes to the Octave source, send them as context diffs. If you even discuss something in the Octave source, refer to it by context, not by line number, because the line numbers in the development sources probably won't match those in your sources.

Here are some things that are not necessary:

• A description of the envelope of the bug. Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it. Such information is usually not necessary to enable us to fix bugs in Octave, but if you can find a simpler example to report instead of the original one, that is a convenience. Errors in the output will be easier to spot, running under the debugger will take less time, etc. Most Octave bugs involve just one function, so the most straightforward way to simplify an example is to delete all the function definitions except the one in which the bug occurs. However, simplification is not vital; if you don't want to do this, report the bug anyway and send the entire test case you used.
• A patch for the bug. Patches can be helpful, but if you find a bug, you should report it, even if you cannot send a fix for the problem.

Sending Patches for Octave

If you would like to write bug fixes or improvements for Octave, that is very helpful. When you send your changes, please follow these guidelines to avoid causing extra work for us in studying the patches.

If you don't follow these guidelines, your information might still be useful, but using it will take extra work. Maintaining Octave is a lot of work in the best of circumstances, and we can't keep up unless you do your best to help.

• Send an explanation with your changes of what problem they fix or what improvement they bring about. For a bug fix, just include a copy of the bug report, and explain why the change fixes the bug.
• Always include a proper bug report for the problem you think you have fixed. We need to convince ourselves that the change is right before installing it. Even if it is right, we might have trouble judging it if we don't have a way to reproduce the problem.
• Include all the comments that are appropriate to help people reading the source in the future understand why this change was needed.
• Don't mix together changes made for different reasons. Send them individually. If you make two changes for separate reasons, then we might not want to install them both. We might want to install just one.
• Use diff -c or diff -u to make your diffs. Diffs without context are hard for us to install reliably. More than that, they make it hard for us to study the diffs to decide whether we want to install them. If you have GNU diff, use diff -cp, which shows the name of the function that each change occurs in.
• Write the change log entries for your changes. Read the ChangeLog file to see what sorts of information to put in, and to learn the style that we use. The purpose of the change log is to show people where to find what was changed. So you need to be specific about what functions you changed; in large functions, it's often helpful to indicate where within the function the change was made. On the other hand, once you have shown people where to find the change, you need not explain its purpose. Thus, if you add a new function, all you need to say about it is that it is new. If you feel that the purpose needs explaining, it probably does--but the explanation will be much more useful if you put it in comments in the code. If you would like your name to appear in the header line for who made the change, send us the header line.