Make explicit when a struct is truthy or falsy in C++

Question

I have defined a simple struct mystruct in C++. I would like to be able to use

mystruct a; 
// do things to a
if(a) { 
    /* do things */ 
}

directly. Is there a way for me to define the behavior of this?

Write a explicit operator bool for your class and figure out what it means to be true. — NathanOliver, Nov 01 '16 at 18:36

score 4 · Accepted Answer · edited May 23 '17 at 12:19

4

Is there a way for me to define the behavior of this?

Yes, provide an overload for the bool type conversion operator:

class mystruct {
public:
  explicit operator bool () const {return condition; } // This is the conversion operator
};

This answer contains some more detailed info.

edited May 23 '17 at 12:19

Community

answered Nov 01 '16 at 18:37

Thank you! I figured it would be something like this, but did not know the terminology to google it. – Mees de Vries Nov 01 '16 at 18:40
@MeesdeVries Totally understandible. The terminology gap is often a bigger problem than the problem you're solving. – user4581301 Nov 01 '16 at 18:45
I believe the `explicit` keyword (or the safe bool idiom for everyone who is stuck with a pre-C++11 compiler) should be mentioned, because it avoids a bunch of annoying problems of the non-explicit version. It’s part of the linked answer, but I believe it’s an important enough issue to at least mention it here as well. – besc Nov 01 '16 at 20:19
@besc Besides it's mentioned in the linked detailed info, i've added that to my sample. – πάντα ῥεῖ Nov 01 '16 at 20:21

1 Answers1