Static Variables

[Anmol444]

From my book


"There are some things you can’t do with automatic variables within a function. You can’t count how many times a function is called, for example, because you can’t accumulate a value from one call to the next. There’s more than one way to get around this if you need to. For instance, you could use a reference parameter to update a count in the calling program, but this wouldn't help if the function was called from lots of different places within a program."

How will it not help if the function is called from many places in the program?

Is it because maybe the scope of the variable used will end?

[Yanson]

I think it means if you call the function from within another function, it might not be possible to pass the same variable to the function.

[Anmol444]

No but you are taking it as a reference, you should be able to.

[giblit]

maybe he means that you can actually keep track of the number of times a function is called by using a static variable try this

void staticFunction( void )
{
    static short calls = 0; //static is only initialized once kind of like a global
    calls++;
    std::cout << "This function has been called " << calls << " times!" << std::endl;
}

void autoFunction( void )
{
    short calls = 0; //gets initialized each time
    calls++;
    std::cout << "This function has been called " << calls << " times!" << std::endl;
}

int main( int argc , char** argv )
{
    for( unsigned int i = 0; i < 10; i++ )
    {
        staticFunction();
    }

    for( unsigned int i = 0; i < 10; i++ )
   {
        autoFunction();
    }
}

I'm not sure exaclty what he means maybe he means like it will seem like it jumps if it is called a bunch of times in different functions at one time maybe?

[Anmol444]

Also he means without it being static, without calls being static lol.

[giblit]

Oh ya I wasn't really reading it all I.just saw static

[Daleth]

void funky(int &count){
   count++;
   std::cout << "I have been called " << count << " times so far..." << std::endl;
}
void funky2(){
   int callnumber(0);
   for(int I=0; I < 20; I++)   funky(callnumber);
}
void funky3(){
   int callnumber(0);
   for(int I=0; I < 5; I++)   funky(callnumber);
}

So what is the total number of times funky has been called? Is it 20? 5? Or 25?
Without using static variables, the message printed out from funky is misleading.

[Anmol444]

Why dont you just make the call number a variable in main function?

That would make it accurate, throughout, I am still leaning towards if its scope ends.

[Daleth]

void Shoot(int& inum){
   if(inum > 0){
      std::cout << "PEW" << std::endl;
      inum--;
   }else   std::cout << "Click..." << std::endl;
}

class Gunman{
   public:
   Gunman():bullets(6){}
   void FireGun(int& baton){
        Shoot(baton);
   }
   private:
   int bullets;  //Useless :(
};
class Investigator{
   public:
   void Count_Number_of_Shots(int& baton){
      std::cout << "Number of shots fired: " << baton << std::endl;
   }
};
int main(){
   int b;  //The way this is used is similar to global variables --> not a good idea
   Gunman man[2];
   Investigator PoorSap;
      //Empty guns
   for(int I = 0; I < 6; I++){
      man[0].FireGun(b);
      man[1].FireGun(b);
   }
   PoorSap.Count_Number_of_Shots(b);
}

Shouldn't each gunman fire off six shots?
Why would you want to make all of your functions take reference variables. You are needlessly making them dependent on a sole source.
This is like using global variables because every function uses it.

Edit:
I suppose my example also shows indirect coupling between the two classes.

[Anmol444]

Ill look at it tomorrow gnite

[Zaita]

How will it not help if the function is called from many places in the program?

It won't help because then you have to continuously pass around a variable to all of the objects called "howManyTimesXHasBeenCalled". It's possible, but impractical because of the amount of overhead code you would have to write.

If I have 100 objects calling a "print" method everyone of them would have to have the same howManyTimesPrintHasBeenCalled variable to pass in to it. When I could just make a static variable in the print method.

[Anmol444]

Alright thanks Zaita!

Thanks Daleth for your help, your examples were nice!