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Comment by michaelochurch | Hacker News Reader

In examples, magic numbers are OK. It's in large production systems (that will require tuning, which becomes impossible with "magic numbers") that they're a code smell. I'd much rather, in a small example, see:

    new int[2048];

than

    #define TWENTYFORTYEIGHT 2048
    new int[TWENTYFORTYEIGHT];

Also, it's generally OK to use a "magic number" if you know that the constant will only be used in that one place, or that there is no way it will ever change. Where they're bad is when they represent undocumented constraints across a program (i.e. "this 64 and that 64 are the same and can't be changed independently".)

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In my experience, aliasing numbers to words has never improved any code in any way whatsoever, and sometimes causes more headaches since numbers are easy and natural to reason about numerically (big surprise...), while values such as TWENTYFORTYEIGHT impose more mental overhead and open you up to typos.

It strikes me as a symptom of the "magic numbers are evil witchcraft" religion gone to the extreme. The whole point of banishing magic numbers is to improve code's clarity and robustness to change. I've seen

  #define ZERO 0

and

  #define ONE 1

more times than I care to admit. I have yet to see the value of either change.

Programmers that replace 0 with ZERO, 1 with ONE, and 2048 with TWENTYFORTYEIGHT are severely misunderstanding why magic numbers are a bad thing in the first place. TWENTYFORTYEIGHT means exactly the same thing as 2048 (that is to say, TWENTYFORTYEIGHT means roughly nothing), but replacing 2048 with a symbolic constant that actually means something (say, BUFFER_SIZE) is a good idea.

I would say ONE_TB is an improvement over 1099511627776 when it comes to "natural to reason about" numbers, but yes, defining ZERO and ONE is moronic.

A lot of times TiB is spelled 1024 * 1024 * 1024 * 1024 or 1 << 40, relying on compile-time constant folding to compute the final value. I usually find that a lot more readable than remembering the actual number.

#define M_PI 3.14159265358979323846 is usually nicer than seeing (and possibly mistyping) those digits of pi each time.

Yeah, we were always taught that zero, one, empty string and other "edge case" values were O.K. to have in code directly. I'm inclined to agree.

Tell me what the number represents rather than what the value of the number is. How about this?

    #define BUFFER_LENGTH 2048
    new int[BUFFER_LENGTH];

And Standard C already defines a constant you can use: BUFSIZ.

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