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When to use int, const int, const byte and Define

colporteur

I'm not a programmer. I am more of a ressurectionist. I find Arduino code pieces and join them together to make a program like Dr. Frankenstein joined body parts to create his monster. 

I see the statements listed in the question and wondered when do they apply. In collecting code parts from a number of programs, I can develop a program that has all four before the voids.  If I was to create a program from scratch I'm not confident I know what one to select for the variable type I am using.

Are there some best practices a novice could use in applying these to get the most benefit from their programming?

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  • Personally, I used to only use #define for text-replacement. So, things like #define NOT_PRESSED 0x1, and #define PRESSED 0x0 for buttons. It makes if-statements more readable. For example, (if digitalRead(pin) == NOT_PRESSED.) Good solution for people who mistakenly think that pull-ups make the inputs inverted.

    In the past, I would always define things like pin functions as a const. But lately, I've been using #defines more. For any value that will fit into an 8-bit number, there is no performance difference between a #define macro or a const (of an 8-bit variable type.) For a const that fits into a register, most compilers won't bother treating it as a variable anyway.

    As usual, it is more important to be consistent in your code than get worked up over which is better.

    Regarding int versus byte, versus, whatever, except for byte and char, I have stopped using types like int. Instead, I use fixed-width integer types like uint8_t or uint32_t or int8_t. These are all part of stdint.h.

    Using fixed width removes the ambiguity of "How big is this variable on this processor with this compiler on this week of the year?"

  • in reply to baldengineer

    Definitely the fixed width types, otherwise I find myself in the situation JWx mentions: at least .... and off we go to the races to find out what size is actually is.

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