"static const" vs "#define" vs "enum"

user_134713 0
Viewed 381224

Which one is better to use among the below statements in C?

static const int var = 5;

or 

#define var 5

or

enum { var = 5 };
constants c
17 Answers

Another drawback of const in C is that you can't use the value in initializing another const.

static int const NUMBER_OF_FINGERS_PER_HAND = 5;
static int const NUMBER_OF_HANDS = 2;

// initializer element is not constant, this does not work.
static int const NUMBER_OF_FINGERS = NUMBER_OF_FINGERS_PER_HAND 
                                     * NUMBER_OF_HANDS;

Even this does not work with a const since the compiler does not see it as a constant:

static uint8_t const ARRAY_SIZE = 16;
static int8_t const lookup_table[ARRAY_SIZE] = {
    1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16}; // ARRAY_SIZE not a constant!

I'd be happy to use typed const in these cases, otherwise...

user_1088020

Incidentally, an alternative to #define, which provides proper scoping but behaves like a "real" constant, is "enum". For example:

enum {number_ten = 10;}

In many cases, it's useful to define enumerated types and create variables of those types; if that is done, debuggers may be able to display variables according to their enumeration name.

One important caveat with doing that, however: in C++, enumerated types have limited compatibility with integers. For example, by default, one cannot perform arithmetic upon them. I find that to be a curious default behavior for enums; while it would have been nice to have a "strict enum" type, given the desire to have C++ generally compatible with C, I would think the default behavior of an "enum" type should be interchangeable with integers.

user_3637510

I am not sure if I am right but in my opinion calling #defined value is much faster than calling any other normally declared variable (or const value). It's because when program is running and it needs to use some normally declared variable it needs to jump to exact place in memory to get that variable.

In opposite when it use #defined value, the program don't need to jump to any allocated memory, it just takes the value. If #define myValue 7 and the program calling myValue, it behaves exactly the same as when it just calls 7.

user_77811950
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