Correct way to call a singleton object in C++

Question

I've build a singleton class based on the hit posted here.

I've extended it with a getMessage() function, that will retrive an internal dictionary message - the dictionary needs to be loaded only once on the whole application, that is the reason of the singleton.

My code:

Singleton.hpp

class Singleton {

public:

    static Singleton& getInstance();
    std::string getMessage(std::string code);

private:

    Singleton() {}; 
    Singleton(Singleton const&) = delete;
    void operator=(Singleton const&) = delete;
};

Singleton.cpp

Singleton& Singleton::getInstance()
{
    static Singleton instance;
    return instance;
}


std::string Singleton::getMessage(std::string code)
{
    /// Do something
    return "Code example.";
}

And the main code:

main.cpp

int main()
{
        Singleton* my_singleton;
        my_singleton = Singleton::getInstance(); **<-- ERROR HERE**

        cout << my_singleton->getMessage("a"); << endl

}

Main is giving me an error: Cannot convert 'Singleton' to 'Singleton*' in assignment

What is the correct way to "instantiate" the singleton and make use of the getMessage function.

Thanks a lot for helping...

you might want to look at this silviuardelean.ro/2012/06/05/few-singleton-approaches — Angel Angel
– Angel Angel, Commented Apr 23, 2015 at 0:17
For Singleton* my_singleton2; if you print &my_singleton and &my_singleton2, it will be different? — user2748107
– user2748107, Commented Dec 22, 2021 at 20:49

Christian Abella · Accepted Answer · 2015-04-23 00:05:00Z

6

what about you just call the function like this:

Singleton::getInstance().getMessage("a");

instead of assigning it to a variable.

edited Apr 23, 2015 at 0:05

answered Apr 22, 2015 at 23:47

Christian Abella

5,7872 gold badges33 silver badges42 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Mendes Over a year ago

Doesn´work and doesn´t make sense that I cannot store it in a variable...I need to fix howto store it in a variable, not to avoid it...

Mendes Over a year ago

Actually this gave me a hint on how to solve it... Singleton& my_singleton = Singleton::getInstance(); then my_singleton.getMessage("a");

SHR Over a year ago

@Mendez no need the reference: just type it as: Singleton::getInstance().getMessage("a"); if you want to short it use a macro: #define theSingleton Singleton::getInstance() and use it with the macro: theSingleton.getMessage("a");

KompjoeFriek · Accepted Answer · 2015-04-22 23:42:50Z

2

You want to store a reference to your singleton, not a pointer.

Singleton& my_singleton = Singleton::getInstance();

answered Apr 22, 2015 at 23:42

KompjoeFriek

3,9501 gold badge26 silver badges42 bronze badges

4 Comments

Mendes Over a year ago

Not worked. Compiler generated error 'singleton' declared as reference but not initialized and several others on Singleton code...

yachoor Over a year ago

@Mendez You need to declare it and initialize in the same expression like in the code above

KompjoeFriek Over a year ago

I'm using the exact same Singleton in my own code all the time, it should work. But i prefer to access it like @Christian (and with a dot instead of ->)

KompjoeFriek Over a year ago

@Mendez Please see that my answer does work in this online example: tutorialspoint.com/…

Collectives™ on Stack Overflow

Correct way to call a singleton object in C++

2 Answers 2

3 Comments

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related