RE: [avr-gcc-list] (no subject)

[MuRaT KaRaDeNiZ]

Hi Dave,

My header looks like this:

#ifndef GLOBAL_H
#define GLOBAL_H

u08 tx_packet_length=0;
u08 header_ok=0;
u08 RX485_oldbyte3, RX485_oldbyte2, RX485_oldbyte1;

#endif


I wait from conditional definition, that it  protects from multiple
definitions, and if I include the header, no extern should be needed,
right?

Still,
u08 RX485_oldbyte3, RX485_oldbyte2, RX485_oldbyte1; //does not cause any
error


u08 tx_packet_length=0;
u08 header_ok=0;                //gives multiple definition error , when
header is included in multiple  project files



My problem is still unanswered, what is this?


Best Regards

Murat Karadeniz
http://www.onlinefavbar.com/mukas


-----Original Message-----
From: Dave Hylands [mailto:address@hidden 
Sent: Monday, January 30, 2006 9:30 PM
To: MuRaT KaRaDeNiZ
Cc: AVR-GCC-list
Subject: Re: [avr-gcc-list] (no subject)


Hi,

Sending to list...

> I live a problem with avr gcc: When i use a global variable in the 
> header file and simultaneously initialize it to nonzero value in the 
> declaration, then the use of this header file in multiple project 
> source files as an include causes "multiple definition error" on this 
> specific lines in the header file. Not initialized globals (by myself)

> and defines do not cause any error.  the whole header file content  is

> in a conditional define, in a regular manner, so  i dont understand 
> what is going on. what is wrong?

In the header file, you need to use the word extern.

Putting:

   int x;

says to allocate storage for an int sized variable named x. Since this
is in a header file, every C file that includes the header file will try
to create a variable named x, which is where the multiple declarations
are coming from.

Using:

   extern int x;

says that somebody else has allocated storage for an int sized variable
named x.

--
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/