Shriramana Sharma wrote:
> 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.
Default parameter values need to be constants; if you declare
lawCloseEngine as "const int", you won't get an error.
If you want the default value to be a variable rather than a constant,
you need to use something like:
int lawCloseEngine ( int engineID = -1 ) ;
int lawCloseEngine ( int engineID )
{
if (engineID == -1)
engineID = lawCurrentEngine ;
...
}
Alternatively, define separate zero-arguments and one-argument
versions of lawCloseEngine.
--
Glynn Clements <glynn@xxxxxxxxxxxxxxxxxx>
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