Multiple declaration problem

[Shriramana Sharma <samjnaa@xxxxxxxxx>]

Hello. I have a problem with multiple declaration in a project I am 
working on. I have constructed a similar testcase which throws the same 
kind of error. Please see the files in the attachment. -g or -g3 did not 
give any useful debugging symbols, I don't know why. The following is 
the session transcript:

$ ls
main.cpp  myheader.cpp  myheader.h
$ g++ -c main.cpp
$ g++ -c myheader.cpp
$ g++ -o main main.o myheader.o
myheader.o:(.data+0x0): multiple definition of `b'
main.o:(.data+0x0): first defined here
collect2: ld returned 1 exit status
$ mv main.cpp main.c
$ mv myheader.cpp myheader.c
$ rm *.o
$ gcc -c main.c
$ gcc -c myheader.c
$ gcc -o main main.o myheader.o
myheader.o:(.rodata+0x0): multiple definition of `a'
main.o:(.rodata+0x0): first defined here
myheader.o:(.data+0x0): multiple definition of `b'
main.o:(.data+0x0): first defined here
collect2: ld returned 1 exit status

In my project, I need to put the following statement in a header file:

int lawCurrentEngine = NONE ; // NONE has been enum-med previously

because I need to declare a function

int lawCloseEngine ( int engineID = lawCurrentEngine ) ;

I include the header file containing these two lines in two cpp files, 
and I get a multiple definition error for lawCurrentEngine just like in 
the given test case. If I push the lawCurrentEngine declaration to one 
of the cpp-s (it's not needed in the other cpp) I am unable to provide 
the default argument for the lawCloseEngine which can be done only in 
the header.

I don't understand how I am getting such an error when I have used the 
#ifndef #define #endif technique as per good programming practice.

Please help,

Thanks.

Shriramana Sharma.

Attachment: multiple-declaration-problem.tar.gz
Description: application/gzip