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Finding What's Changed in Your Code

You (or someone else) rolled out a new version of an application and it's behaving…oddly. You ask the people involved (or yourself) "What changed?" and the answer you get is "Nothing." This is, of course, not true. Users do this to us all the time though the question we ask is slightly different ("What did you do differently?", "Nothing").

Of course, the answer we're really giving is "Nothing relevant," which isn't quite the same thing as "Nothing." In both cases, the person asking the question has unconsciously edited out of recollection anything that doesn't seem relevant to the problem. The only solution is to force ourselves to look at everything that changed, rather than just "what's relevant" (it's like looking for something you've lost: Once you've looked in all the places where it should be then you have to look at all the places where it shouldn't be).

Your source control system should be able to tell you all the lines of code that have changed between one version of your code and another. If you're not using a source control system, you can use Visual Studio's Compare Files option, though it's hard to get to in more recent versions of Visual Studio. To compare two files without source control, first click in the Command window (if the window isn't open, use View | Other Windows | Command Window to open it). In the Command window, type this:

Tools.DiffFiles <filename1> <fileName2>

That command isn't as bad as it looks: As soon as you start typing a file name, you'll get IntelliSense support to finish off the file's name. After you hit the Enter key, the command will open a tab with two panes showing both files with your changed/added/deleted lines highlighted.

Of course, even when you find the changed lines you have to stop thinking "Oh, well that can't be the problem." Yes, it can. In fact, it probably is.

Posted by Peter Vogel on 03/15/2018 at 2:16 PM


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