What is the difference between static const and const?

Question

What is the difference between static const and const? For example:

static const int a=5; const int i=5; 

Is there any difference between them? When would you use one over the other?

Answer 1

static determines visibility outside of a function or a variables lifespan inside. So it has nothing to do with const per se.

const means that you're not changing the value after it has been initialised.

static inside a function means the variable will exist before and after the function has executed.

static outside of a function means that the scope of the symbol marked static is limited to that .c file and cannot be seen outside of it.

Technically (if you want to look this up), static is a storage specifier and const is a type qualifier.

Answer 2

The difference is the linkage.

// At file scope static const int a=5;  // internal linkage const int i=5;         // external linkage 

If the i object is not used outside the translation unit where it is defined, you should declare it with the static specifier.

This enables the compiler to (potentially) perform further optimizations and informs the reader that the object is not used outside its translation unit.