Can't call a static method in Qt

Question

I have a simple class containing a static attribute. There are two static methods in this class: one to get the static attribute and the other to initialize it. Yet when call the static method the compiler reports an error.

The class:

class Sudoku {
    Cell Grid[9][9];
    int CurrentLine;
    int CurrentColumn;

    void deleteValInColumn(int val, int col);
    void deleteValInRow(int val, int row);
    void deleteValInBox(int val, int x, int y);
    static int unsetted; //!
public:
    static void IniUnsetted() { //!
        unsetted = 0;
    }
    static int GetUns() { //!
        return unsetted;
    }
    Sudoku(ini InitGrid[9][9]);
    void Calculate_Prob_Values();
    Cell getCell(int x, int y);
    QVector<int> getPossibleValues(int x, int y);
    bool SolveIt();
};

This is the error I get:

In member function 'bool Sudoku::SolveIt()':
no return statement in function returning non-void [-Wreturn-type]
In function `ZN6Sudoku6GetUnsEv':
undefined reference to `Sudoku::unsetted` error: ld returned 1 exit status

Try putting `unsetted` in the `cpp` file: `int Sudoku::unsetted = 0` — Adri C.S., Dec 18 '13 at 13:38
You'll probably find the answer [here](http://stackoverflow.com/q/12573816/1782465). — Angew is no longer proud of SO, Dec 18 '13 at 13:40
@AdriC.S.: no, that is unnecessary. It is zero initialized by default! — László Papp, Dec 18 '13 at 13:41
@LaszloPapp Well, the answer to the OP's question is the last point in the second answer to the Q I posted. — Angew is no longer proud of SO, Dec 18 '13 at 13:42
@LaszloPapp It may be zero-initialised, but it still **needs a definition** in a .cpp file, which the OP obviously doesn't provide. So the `= 0` is unnecessary, but the definition itself it needed. — Angew is no longer proud of SO, Dec 18 '13 at 13:42
@Angew: which is exactly what my answer does now as well. The initialization is still unnecessary to suggest. — László Papp, Dec 18 '13 at 13:53

László Papp · Accepted Answer · 2013-12-18T13:47:22.837

7

You will need to define the static variable, even if it is not initialized explicitly. That is what is missing in your code. You should have provided a simple example to reproduce the issue, but for your convenience I am providing one which works.

main.cpp

class Foo {
    public:
        static int si;
        static void bar();
};

int Foo::si = 0; // By default, it will be initialized to zero though.

void Foo::bar() {
     Foo::si = 10;
};

int main()
{
    Foo::bar();
    return 0;
}

Note: I would suggest to get someone to review your code because "unsetted" is incorrect English. If we are at it, you would probably need to fix your indentation as well.

edited Dec 18 '13 at 13:47

answered Dec 18 '13 at 13:40

László Papp

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If I'm wrong, then explain [this](http://ideone.com/oyLOag), please. It's not about initialisation, it's about a definition. Non-const static class members need one, period. – Angew is no longer proud of SO Dec 18 '13 at 13:47
This work just fine Note : initialization and definition should be in .CCP file . Thank you all . شكرا – Oussaki Dec 18 '13 at 14:01
@LaszloPapp Now, no problem (note that I've long since removed the downvote). See my comment 17 mins ago. – Angew is no longer proud of SO Dec 18 '13 at 14:02

score 5 · Answer 2 · answered Dec 18 '13 at 13:42

In your code there is no definition of unsetted, there is only declaration.

The solution is to put somewhere in your cpp file a line like this:

int Sudoku::unsetted

The reason for that is that each instantiation of Sudoku class will use the same unsetted member so it cannot be defined for each of them, so it's up to programmer to define it in one place only.

score 2 · Answer 3 · answered Dec 18 '13 at 13:42

2

In your cpp file, define the static variable (ideally with an initialization):

int Sudoku::unsetted = 0;

answered Dec 18 '13 at 13:42

codeling

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The problem is not in the initialization . the problem is in the definition it self . thank you the problem is solved . – Oussaki Dec 18 '13 at 14:14

score 2 · Answer 4 · edited Mar 06 '17 at 13:14

2

If you are declaring any static variable in class, then you should define that variable outside the class also.

Example:

class A
{
    public:
    static int x;    // declaration
};

int A::x;            // definition

edited Mar 06 '17 at 13:14

codeling

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answered Dec 18 '13 at 13:42

rajenpandit

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2

It's not "defining" and "initialize," but "declaring" and "define." – Angew is no longer proud of SO Dec 18 '13 at 13:45

Can't call a static method in Qt

4 Answers4

main.cpp