Unexpected static counter variable behaviour

Question

Lately I tried getting my head around the static keyword and here I attempt to simply use the static keyword for a variable declaration within a function. Like so:

void counter()                                                                                        
{                                                                                                     
    static int counter = 0; //should be initialized only once and once only                           
    counter++; //increment for every call of this function                                            
}

I understand that due to the variable being static, it will live outside the function and therefore from wherever I decide to print out counter, it should give me the number of times the function counter() was called. So I did a simple test as shown:

int main()                                                                                            
{                                                                                                     
    for(unsigned int i = 0; i < 10; i++){                                                             
        counter();                                                                                    
    }                                                                                                 
    std::cout << counter << std::endl;                                                                

    return 0;                                                                                         
}

From this test I expected to get number 10... but instead the number of counts the code returned was 1.

Please, what am I missing here?

I found other submissions to "similar" issues such as this one: static counter in c++ But they mostly revolve around the static keyword being used in classes.

`std::cout << counter` versus `std::cout << counter()`. Just a typographical error. — Dark Falcon, Nov 17 '17 at 01:42
But I was not trying to print the function `counter()` that would return nothing as its void, instead I'm printing the static variable `counter` defined in the function `counter()` — miro_x, Nov 17 '17 at 01:45
The static variable `counter` is accessible only inside the function `counter()`. Outside of it, the **identifier** `counter` refers to the function. — Sam Varshavchik, Nov 17 '17 at 01:46
You are not printing `counter`. See this answer https://stackoverflow.com/a/2064722/1143634 — , Nov 17 '17 at 01:46
a static local variable can only be called in that local scope, it cannot be called outside. — Lorence Hernandez, Nov 17 '17 at 01:46
Thank you for the quick replies. I assumed from the C++ documentation I read that static variables remain in memory once initialised and that they remain in memory until the program terminates. But I guess that means I can't just violate the rules of namespaces like I just did. — miro_x, Nov 17 '17 at 01:50
Whether or not something "remains in memory" is completely independent of what the scope of the object's identifier is. — Sam Varshavchik, Nov 17 '17 at 01:51
So in my code what is the number 1 that it returns, it seems from the link that @Ivan gave I am just accessing the function reference? So the function reference is 1? I am still not very clear on that front. — miro_x, Nov 17 '17 at 01:55
@mira_x you are trying to print function address, but it cannot be simply printed using `std::ostream`, so it is converted to `bool` implicitly. So your code essentially prints `true` all the time. GCC will warn you if you enable warnings `-Wall -Wextra`. — , Nov 17 '17 at 01:58

score 2 · Answer 1 · answered Nov 17 '17 at 01:47

2

counter is still a local variable inside void counter() so you still need to return it.

answered Nov 17 '17 at 01:47

Ahmed Karaman

523
3
12

score 2 · Accepted Answer · answered Nov 17 '17 at 01:49

You are printing counter in main(), where it wasn't declared. Just because you declared it as static in counter() doesn't mean you can access it in main().

If you do :

void counter() {
    static int counter = 0;
    std::cout << counter++ << std::endl;
}

int main() {
    for(unsigned int i = 0; i < 10; i++){
        counter();
    }
    return 0;
}

You can see the counter incrementing.

Unexpected static counter variable behaviour

2 Answers2