[galib] linker error when including ga.h (or GA1DArrayGenome.h)

Aaron Hoover ahoover at eecs.berkeley.edu
Sat Apr 21 18:17:35 EDT 2007

Hi all,

I'm get the following error in my code when I include the ga.h or the  
GA1DArrayGenome.h file:

/usr/bin/ld: Undefined symbols:
int operator==<OpenMesh::EdgeHandle>(OpenMesh::EdgeHandle const&,  
OpenMesh::EdgeHandle const&)
int operator==<OpenMesh::FaceHandle>(OpenMesh::FaceHandle const&,  
OpenMesh::FaceHandle const&)
int operator==<OpenMesh::VertexHandle>(OpenMesh::VertexHandle const&,  
OpenMesh::VertexHandle const&)
int operator==<OpenMesh::HalfedgeHandle>(OpenMesh::HalfedgeHandle  
const&, OpenMesh::HalfedgeHandle const&)
int operator!=<OpenMesh::HalfedgeHandle>(OpenMesh::HalfedgeHandle  
const&, OpenMesh::HalfedgeHandle const&)
collect2: ld returned 1 exit status

The problem seems to be related to how templates are instantiated.  
The OpenMesh::EdgeHandle data structure is a template that inherits  
from a standard vector, and of course doesn't have (or need to have)  
an int operator== defined for it. It seems that somehow the  
GA1DArrayGenome (or some other template in ga.h) has overridden that  
operator, but now the linker is looking for definitions of that  
operator in other templates.

A couple of other things I should mention: I am team developing with  
someone who uses VC++ 7.0 (I'm using XCode/gcc/g++ toolchain on a  
mac) and he does not get this error compiling the same exact code.  
This is leading me to suspect that it has something to do with how VC+ 
+ compiler hands automatic template instantiation as compared to gcc/g 
++ and ld. Therefore, I'm hoping this can be fixed with a simple  
compiler flag, but I don't know what that flag should be. Using -fno- 
implicit-templates created a lot of other errors because it's very  
difficult for me to know all the templates that will be necessary and  
instantiate them manually.

Any help anyone can offer, is greatly appreciated.

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