C++ Making my class accept the << operator

Question

I'm writing a simple debug utility class:

class MyDbg {
  protected:
    std::string filename;
    std::ostream* fp;
    std::ofstream fout;

  public:
    void setOutFile(std::string filename) {
      if(filename == "terminal") {
        fp = &std::cout;
      } else {
        fout.open(filename);
        fp = &fout;
      }
    }

What I want to do is be able to set an instance of this to either std::cout or to output to a file. And then be able to stream to an instance of this object as if I were streaming to std::cout (or an ofstream):

So the object should be able to take the <<() operator and support an input stream (like an stringstream) or basic types (like integer, char, etc.).

int main() {
  MyDbg dbg;
  dbg.setOutFile("terminal");
  dbg << "foo" << std::endl;
  dbg.setOutFile("dbg.log");
  dbg << "bar" << std::endl;
}

I'm thinking this would require me to write my own stream child class? Does that sound about right? Or is there a way to overload an operator to do this?

You need to overload `operator<<` - there should be sufficient examples of doing that online — UnholySheep, Sep 14 '21 at 08:05
What you need is to overload `operator<<()` for your type (`MyDbg`) — Ghasem Ramezani, Sep 14 '21 at 08:05
"require me to write my own stream child class?" ... forget about inheritance, thats the wrong path. All you need is a `MyDbg::operator<<` that takes the input and pipes it to a file — 463035818_is_not_an_ai, Sep 14 '21 at 08:06
I mean there is a bit of inheritance in the standard library with iostreams, but you don't need to dig that deep — 463035818_is_not_an_ai, Sep 14 '21 at 08:07
You can reuse a lot of `ostream` and `streambuf` functionality if you inherit from it [like this](https://stackoverflow.com/questions/772355/how-to-inherit-from-stdostream). — rustyx, Sep 14 '21 at 08:08
As an aside, common Unix convention is to use "-" as the "filename" for stdout. — Sebastian Redl, Sep 14 '21 at 08:08
@463035818_is_not_a_number `operator<<()` can't be a member function. — sweenish, Sep 14 '21 at 12:29
@sweenish why not? https://godbolt.org/z/EnnbPYnd3. I guess you are talking about the `ostream`s `operator<<`, but as I understand the question, OP wants a `MyDbg::operator<<` (see their `main`) — 463035818_is_not_an_ai, Sep 14 '21 at 12:30
@463035818_is_not_a_number I guess I should read the question more carefully. I went straight to the idiomatic case. — sweenish, Sep 14 '21 at 14:53

C++ Making my class accept the << operator

0 Answers0