C++ singleton LNK2019 error

Asked Feb 19 '17 at 08:04

Active Feb 19 '17 at 08:14

Viewed 135 times

I'm trying to write a singleton in c++ - but I got LNK2019 error:

Severity Code Description Project File Line Error LNK2019 unresolved external symbol "private: __thiscall DBWriter::DBWriter(void)" (??0DBWriter@@AAE@XZ) referenced in function "public: static class DBWriter * __cdecl DBWriter::getInstance(void)" (?getInstance@DBWriter@@SAPAV1@XZ) ORCompare

Can someone help me find my mistake?

Here is the h. file:

#pragma once
#ifndef DBWRITER
#define DBWRITER

 class DBWriter
{

public:

    ~DBWriter();
    static DBWriter* getInstance();

private:
    DBWriter();

    static DBWriter *dbwriter;
};

#endif //DBWRITER

and the .cpp file:

#include "DBWriter.h"

DBWriter * DBWriter::getInstance()
{
    if (dbwriter == NULL)
        dbwriter = new DBWriter();
    return dbwriter;
}

I'll be happy if someone can explain me my mistake. Thank you.

edited Feb 19 '17 at 08:14

asked Feb 19 '17 at 08:04

STF

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1

Provide the _full_ error message. Are you defining your constructor and destructor? – Greg Kikola Feb 19 '17 at 08:07
I didn't add nothing else to the code – STF Feb 19 '17 at 08:15
@πάντα ῥεῖ - I don't understand why you think it's the same question it is not the same problem!!! – STF Feb 19 '17 at 08:16
@STF Where's your defintion of `dbwriter`? – πάντα ῥεῖ Feb 19 '17 at 08:18
@πάνταῥεῖ in the .h file – STF Feb 19 '17 at 08:33
@STF No, that's a declaration. You have to have a _definition_ also. – πάντα ῥεῖ Feb 19 '17 at 08:36
1

@STF Wrong, you only have a _declaration_ in your header file. `static` members must have a _definition_ somewhere, preferably in the class's source file. – Greg Kikola Feb 19 '17 at 08:36
@GregKikola like "dberiter=NULL"? – STF Feb 19 '17 at 08:52
1

No, like `DBWriter *DBWriter::dbwriter = NULL;` in your .cpp file. That will define `DBWriter::dbwriter`. – Greg Kikola Feb 19 '17 at 09:27
@GregKikola In which function should I add it? – STF Feb 19 '17 at 09:40
@STF Outside of any function. – Greg Kikola Feb 19 '17 at 09:41
@GregKikola so when it will be happen? – STF Feb 19 '17 at 09:47

C++ singleton LNK2019 error

0 Answers0