Static variables in C and C++

Question

Is there any difference between a variable declared as static outside any function between C and C++. I read that static means file scope and the varia

Answer 1

C and C++ are the same.

static does two different things.

For variables declared outside a function scope, it changes the visibility (linkage) of the variable. The variable will be a global variable since it is outside a function scope. If it isn't static, it will have universal linkage (visibility) so any code linked together with this can access it (they may have to declare it extern). If the variable is outside a function scope and is static, it still a global variable in that it always exists and keeps its value, but no code outside the same compilation unit (that .c file and any .h's included) can access it.

For variables declared inside a function scope, static changes the location where the variable is stored. If it is not static, it will be an automatic variable, that means it disappears as the function exits and comes back into existence (on the stack) when the function is entered again. This it loses its value when you exit the function. And also any references to it (pointers to it) are invalid after the function exits. If a variable declared inside a function scope is static, then it makes it not an automatic variable but a globally allocated one. So the variable will exist after the function exits and thus will keep its value across invocations of the function and also any references (pointers) to it are valid even after the function exits. Note that in both cases the scope of the variable is only within that function so it's not possible to access it directly (but only via saved reference) from outside the function scope.

One last thing static does is change when the initializer (i.e. int foo = 5) for the variable is run. For all the cases where the allocation is global (every case except the automatic one), the initializer is run only once, at the beginning of the execution of your program. It is run before main() is run even, so you can get some not quite expected result if your initializer isn't just a constant number but runs some code. For the automatic case, the initializer is run every time the function is entered, and in this case it is always after main() has been entered.