Wed, 08 Aug 2007

Code Craft falls down hard

I know it’s not possible to write a big book without having any errors fall through the cracks, and I don’t make a habit of public excoriation of people for things that can be forgiven — but there are unforgiveable things.

Take Code Craft by Pete Goodliffe, published by No Starch Press as an illustration. Here we have a 580-page tome dedicated to the practice of writing excellent code and on page 13 it has an egregious example of unforgiveable content.

Before getting to the details, I would mention that neither the book nor the website give me any information that I could find in a reasonable amount of time about how to report errata. Had there been such an avenue, I’d have taken it. As it is, this seems the easiest approach.

This is in Chapter 1, On the Defensive, subtitled Defensive Programming Techniques for Robust Code. Under the heading Use Safe Data Structures, he gives the following example of some C++ code:

    char *unsafe_copy(const char *source)
    {
        char *buffer = new char[10];
        strcpy(buffer, source);
        return buffer;
    }

He then gives the correct explanation of the problem with this code when the length of the string in source exceeds 9 characters. After some discussion, he then says it’s easy to avoid this trap by using a so-called “safe operation” and offers this idiotic solution:

    char *safer_copy(const char *source)
    {
        char *buffer = new char[10];
        strncpy(buffer, source, 10);
        return buffer;
    }

In case the reader doesn’t know how the C string library (which is what is being used here, despite the otherwise C++ content) works, let me point out that strncpy is guaranteed not to solve the problem under discussion. The strncpy function will only copy at most the specified number of characters, but — in the critical case where the source string is too long — it will not add the very important NUL-terminator character. And so users of the returned buffer will still fall off the end of it and cause breakage.

Every C or C++ programmer who has been paying attention knows what is wrong with the C string library and knows how to use it correctly. So an error of substance like this should simply never have happened. It’s not a typo. It’s not a trivial error. It’s just plain wrong. And there’s no excuse for it.

I’m sure the author has many good things to say in this book and many of the sentences I have skimmed certainly do make sense. But stuff like this makes it impossible for me to suggest that it has any place on the budding programmer’s bookshelf. That’s a shame, because we need books that do what this book purports to do.

What irritates me most about this is that none of the book’s reviewers spotted this glaring error and none of the online reviews that I found noticed it either. This means that nobody with even a tiny clue has been looking at it.

Posted at: 10:52

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