It's hard to troubleshoot the exact problem without code, but this most often happens when a
variable is declared *and* defined directly in a .h file.
The solution, usually, is to *declare* the variable as "extern type blah;" in the include file
and *define* the variable in one .c file as "type blah = value;".
The linker then ensures that all references to variable "blah" point to that one definition.

unixprgrmr01@gmail.com wrote:
> I am trying to link library xy.a composed of x.o containing function x() and
> y.o containing function y() with d.o giving executable d
> 
> I call both x() and y() from d.cpp.  When I comment out the function call to
> y() in d.cpp it links just fine with library xy.a giving executable d BUT
> when I uncomment the function call to y() I get duplicate variable
> declaration errors.
> 
> Note that I need x.o and y.o in a library because I also link them with e.o
> to give executable e . Both x() and y() are called from both d and e
> executables.
> 
> I use the same custom include files in x.o y.o d.o and e.o. I am getting
> duplicate variable errors from the variables declared in these custom
> include files.
> 
> I also include standard include files such as <stdio.h> and <math.h> etc.
> etc. in all 4 .o's but I don't get duplicate variable errors from these.
> 
> I am #ifndef ing the entire include file just as is done with <stdio.h> etc.
> What am I doing wrong, that at link time I get duplicate variable errors?
> 
> Thanks for your help!
> 
> 
> 
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