CODEWITHSUNDEEP
c++
Nitesh Kartha
Nitesh Kartha

Reputation: 31

What does the :: (scope resolution operator) do in this program?

I am currently learning C++ and saw this program when I was reading a book.

#include <stdio.h>

double counter = 50;

int main(){

for(int counter = 1; counter != 10; ++counter){
  printf("%d\n",::counter/counter);
}

}

Now, I read up on the Scope Resolution Operator and I thought that this would print out the global variable counter divided by the local variable counter. However, the program prints out this:

2094374456

4195758

4195758

4195758

4195758

4195758

4195758

4195758

4195758

What are these numbers and what does the Scope Resolution Operator do in this case?

Disclaimer: I do not know C, but I have extensive experience in Java.

Upvotes: 0

Views: 95

Answers (2)

MikeCAT
MikeCAT

Reputation: 75062

You used wrong format specifier. ::counter will be the global counter, whose type is double, so the result fo division will have type double and it should be printed via %f format specifier or other specifier that calls for double such as %g.

Passing data having wrong type will invoke undefined behavior in C, but I'm not sure about C++.

#include <stdio.h>

double counter = 50;

int main(){

    for(int counter = 1; counter != 10; ++counter){
      printf("%f\n",::counter/counter);
    }

}

Upvotes: 1

Brian Bi
Brian Bi

Reputation: 119477

::counter does indeed refer to the global variable counter. The problem with this code is that the result of the division is of type double since one of the arguments is, and a double value is being passed to an ellipsis where int is expected since the format specifier is %d. This results in undefined behaviour. You need to change it to %f.

Upvotes: 1

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