What is an "operator int" function?

Question

What is the "operator int" function below? What does it do?

class INT {    int a;  public:    INT(int ix = 0)    {       a = ix;    }     /* Starting here: */    operator int()    {       return a;    }    /* End */     INT operator ++(int)    {       return a++;    } }; 

Answer 1

The bolded code is a conversion operator. (AKA cast operator)

It gives you a way to convert from your custom INT type to another type (in this case, int) without having to call a special conversion function explicitly.

For example, with the convert operator, this code will compile:

INT i(1234); int i_2 = i; // this will implicitly call INT::operator int() 

Without the convert operator, the above code won't compile, and you would have to do something else to go from an INT to an int, such as:

INT i(1234); int i_2 = i.a;  // this wont compile because a is private 

Answer 2

operator int() is a conversion operator, which allows this class to be used in place of an int. If an object of this type is used in a place where an int (or other numerical type) is expected, then this code will be used to get a value of the correct type.

For example:

int i(1); INT I(2); // Initialised with constructor; I.a == 2 i = I;    // I is converted to an int using `operator int()`, returning 2.