Qt and global variables

[Lykurg]

Sorry,

maybe I am too stupid, but your code doesn't work for me. I take your code and just changed the name of the class:

#ifndef CONFIGURATION_H
#define CONFIGURATION_H
 
#include <QtCore>
#include <QtSql>
 
class configuration
{
  public:
    static configuration* instance()
    {
      static QMutex mutex;
      if ( !m_instance )
      {
        mutex.lock();
        if ( !m_instance )
          m_instance = new configuration;
        mutex.unlock();
      }
      return m_instance;
    }
 
  private:
  configuration(){};
    configuration( const configuration& _instance ){};
    static configuration* m_instance;
 
// [...] some other functions
 
};
 
configuration* configuration::m_instance = NULL;
 
#endif

#ifndef CONFIGURATION_H
#define CONFIGURATION_H

#include <QtCore>
#include <QtSql>

class configuration
{
  public:
    static configuration* instance()
    {
      static QMutex mutex;
      if ( !m_instance )
      {
        mutex.lock();
        if ( !m_instance )
          m_instance = new configuration;
        mutex.unlock();
      }
      return m_instance;
    }

  private:
  configuration(){};
    configuration( const configuration& _instance ){};
    static configuration* m_instance;

// [...] some other functions

};

configuration* configuration::m_instance = NULL;

#endif

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When compiling I receive the error (which I don't understand == don't know what to do/where the error could be):
.comp/sw_normal.o: In function `operator delete(void*, void*)':
/usr/include/qt4/QtCore/qatomic_i386.h:62: multiple definition of `configuration::m_instance'
.comp/qvortaro.o:/home/lykurg/Programmierung/qvortaro/src/qvortaro.cpp:194: first defined here
collect2: ld returned 1 exit status


And by the way must it in your example in the wiki not be

Singleton* Singleton::m_Instance = 0;

Singleton* Singleton::m_Instance = 0;

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instead of

Singleton* m_Instance = 0;

Singleton* m_Instance = 0;

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Thanks,
Lykurg

P.s: if I comment the function (on bottom of the file) in qvortaro.cpp:194 out, then this error pointed to now last function on the file.

[jacek]

When compiling I receive the error (which I don't understand == don't know what to do/where the error could be):
.comp/sw_normal.o: In function `operator delete(void*, void*)':
/usr/include/qt4/QtCore/qatomic_i386.h:62: multiple definition of `configuration::m_instance'
.comp/qvortaro.o:/home/lykurg/Programmierung/qvortaro/src/qvortaro.cpp:194: first defined here
collect2: ld returned 1 exit status

You have placed the definition of static member variable in a header file, therefore every .cpp file that includes it has it's own copy of that variable. Better move that line to one of the .cpp files, say configuration.cpp.

[Methedrine]

And by the way must it in your example in the wiki not be

Singleton* Singleton::m_Instance = 0;

Singleton* Singleton::m_Instance = 0;

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instead of

Singleton* m_Instance = 0;

Singleton* m_Instance = 0;

To copy to clipboard, switch view to plain text mode 

Yes, of course. Thank you, Lykurg for spotting it, and thank you, jacek, for correcting it before I spotted this thread