Is it possible to print a custom object by passing it to Serial.print()?

Question

I googled about it, but can't find the answer. As I would guess I would have to inherit from the Print class and somehow pass to its print methods the part of my object I would like to be printed. But I am not sure how to go about it or if it is even possible.

Answer 1

There is a class called Printable. If you inherit from that, and implement the size_t printTo(Print& p) function, your object can then be passed to the print functions:

class myClass : public Printable {
 private:
 int _val1;
 int _val2;
 public:
 myClass(int v1, v2) : _val1(v1), _val2(v2) {}
 size_t printTo(Print& p) const {
 size_t r = 0;
 r += p.print("One: ");
 r += p.print(_val1);
 r += p.print(" Two: ");
 r += p.print(_val2);
 return r;
 }
};

Then:

myClass ob(4, 5);
Serial.println(ob);
=> One: 4 Two: 5

• Mykolas: Majenko, thankyou very much for your answer. I got it working. Just little comment on your code. I think instead of "size_t printTo(Print& p)" should be "size_t printTo(Print& p) const". Thankyou
• Majenko: I just copied and pasted the prototype from the header.
• Mykolas: I was getting an error of not overriding virtual function. Once added the const, all ok.
• Majenko: Ok. I have modified it for future reference
• vsz: How are we supposed to know these things? The arduino documentation is quite... lacking... to say the best. Digging through the source code on github?