To create a persistant variable is it better to have a local static variable or a global?

Question

Lets say you have a class (c++) or module (single c file). Then in one of your functions you want to store a copy of a variable and hold its value until the next time the function is called, is it better to have a global (could be private in c++ and not extern'd in c to keep it in the module scope) or make a local static variable?

e.g.:

void some_func_that_does_not_do_anything_useful(int arbVal)
{
    static int lastArbVal = 0;

    if (arbVal > lastArbVal)
    {
        lastArbVal = arbVal;
    }
}

The reason I would make a static is to keep its scope as limited as possible, but certain things I read suggest you should use globals for this, so now I am confused.

What is best (if any)?, pros/cons?

Answer 1

The rule here is simple: if the variable needs to be accessed by more than one functions, make it global. If not, static variables inside functions are usually better. One of the pros is it avoids polluting the global namespace.

Note that if a global variable doesn't need to be accessed outside the file, it's better to declare it as file-scope variable(i.e, declare it as static)

Back to your example, I think it's best to use static variable like you already did.