returning a class from a metod gives wrong values for class variables

Question

My header file contains a class that holds a Boolean and a string

#ifndef RESULT_P
#define RESULT_P

#include <string>
#include <utility>

class MyResult {

public:
    MyResult() = default;
    MyResult( const bool& ok, std::string  msg) : ok_(ok), msg_(std::move(msg)) {}
    explicit MyResult(bool ok) : ok_(ok) {}
    explicit MyResult(std::string msg) : ok_(false), msg_(std::move(msg)) {}

    bool ok() const {
        return ok_;
    }

    void ok(bool ok) {
        ok_ = ok;
    }

    const std::string &msg() const {
        return msg_;
    }

    void msg(const std::string &msg) {
        msg_ = msg;
    }

private:
    bool ok_ { false };
    std::string msg_;

};

#endif

I am using the MyResult(std::string) constructor to create a result that takes by default false on the ok_ method variable.

I am calling

auto result = do_something()

The method do somethings looks like this

   MyResult do_something() {

      if ( something ) {
         //code    } else {
          return MyResult("something wrong happened");    
      }
    }

So returns false and a string. When this method returns and I am calling

cout << result.ok() << endl;

it prints true!!! instead of false. What is wrong?

UPDATE: sorry for my initial version of the post. It prints true, not false.

Please try to create a proper [mcve] to show us, one that replicates the behavior and which we ourselves can copy-paste to try. — Some programmer dude, Oct 30 '19 at 13:01
Your `do_something` function seems to fail to return anything if `something` is `false`. Undefined behavior, or you better post *real* code. — PaulMcKenzie, Oct 30 '19 at 13:02
`MyResult("something wrong happened")` calls the `bool` constructor. Since the pointer to a string literal is never `nullptr` when it is implicitly converted to `bool` it produces `true`. See the duplicate. — François Andrieux, Oct 30 '19 at 13:06

score 1 · Answer 1 · answered Oct 30 '19 at 13:02

1

Using MyResult("something wrong happened"); you are calling this ctor explicit MyResult(std::string msg) : ok_(false), msg_(std::move(msg)) {} then ok_ field is initialized as false.

answered Oct 30 '19 at 13:02

F.Guerinoni

277
2
12

This is incorrect. `MyResult("something wrong happened");` calls the `explicit MyResult(bool)` constructor. See the duplicate. – François Andrieux Oct 30 '19 at 13:08

returning a class from a metod gives wrong values for class variables

1 Answers1