Bitwise or (|) in function argument

Question

I was wondering how to do this:

func(param1|param2|param3)

and then extract those values in the function, I have seen this in multiple functions, or is it better to do this:

func(param1, ...)

?

I am trying to do this in C++, and I was thinking of having the parameters to the function as values in a enum.

How do I solve this?

Answer 1

Param1, param2, param3 are usually defined as a numbers with different bits turned on. | is an operator of bitwise alternative, that means it works on separate bits.

In example:

const int param1 = 0x01;
const int param2 = 0x02;
const int param3 = 0x04;

When you pass an argument to function you make a bitwise alternative of earlier defined params. In function, you don't make a decomposition, but check if a specified bit is set on, using bitwise conjunction:

void func(int arg){
  if(arg & param1)
    // do something
  if(arg & param2)
    // do something else
    // ...
}

func(param1 | param3); 
// "do something" will be done,
// but "do something else" not.

Answer 2

This is an useful example to how create "MessageBox" function with arbitrary button types :

enum Button
{
    OK =      0x0001,
    CANCEL =  0x0010,
    YES =     0x0100,
    NO =      0x1000
};

void messagebox(char *text, int button)
{
    char msg[256];
    strcpy(msg, text);

    if ((button & Button::OK) == Button::OK)
        strcat(msg, " [OK]");
    if ((button & Button::CANCEL) == Button::CANCEL)
        strcat(msg, " [Cancel]");
    if ((button & Button::YES) == Button::YES)
        strcat(msg, " [Yes]");
    if ((button & Button::NO) == Button::NO)
        strcat(msg, " [No]");

    cout << msg << endl;
}

int main()
{
    messagebox("salam", Button::OK | Button::CANCEL);
    return 0;
}