Lifetime of Variables

Lifetime

Two classes of variables …

• Local (“automatic”). Lifetime (and visibility) is confined to the function call.

  • All variables that we had so far are automatic (function parameters are local variables)

• Global (“extern”). Lifetime is the entire program.

  Another point of view: visibility ⟶ later

Global Variables

Global variables are evil

• They obscure program logic

• Side effects through unnecessary persistence

• Global constants are ok

There are use cases though …

• Not a use case: laziness

Global Variables: How?

• Functions (code) can only be defined in global scope

• Have access to local variables and other global objects

int i;

void f(void)
{
    printf("%d\n", i);
}