multiple definitoin of variable

[saman_artorious]

I need to define my queue globally in a header file. And I of course include that header in other classes.
but I constantly receive multiple definition of variable xx.

how can I declare it only once? so for the next times compiler ignores it?

[Santosh Reddy]

You need to define the variable in a cpp file (not in header file).
The header file will have just declaration of the variable with "extern" keyword as prefix, and without intilaization.

[BalaQT]

For extern variable:
ex: extern QList mylist;

For

but I constantly receive multiple definition of variable xx.

Use header guards,
Ex:
#ifndef GLOBAL_H
........
#endif

hope it helps,
Bala

[Santosh Reddy]

For

but I constantly receive multiple definition of variable xx.

Use header guards,
Ex:
#ifndef GLOBAL_H
........
#endif

hope it helps,
Bala

Using guard macro in header file is a good practice, but it will not solve the multiple definition problem/error

[amleto]

I need to define my queue globally in a header file.

no, you don't.

[saman_artorious]

no, you don't.

if queue is defined privately in my class, other object cannot get access to it and enQ. so, I have to set it as global. I cannot pass the QByteArray to the producer of the thread, so that it enQ it to the queue.

[wysota]

if queue is defined privately in my class, other object cannot get access to it and enQ. so, I have to set it as global.

No, you don't have to set it global. But even if you did, you wouldn't do it in a header file as these get included into multiple compilation units causing mutliple declaration problems as the one you're suffering from right now. I think this is a good moment to suggest spending some time with a good book on object-oriented programming before tackling real problems.