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What  separates c++ mangle names from their unmangled versions

Posted on 2006-11-01
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Last Modified: 2008-02-01

I am having trouble linking an application.   I can link using an old .a file, but with the newer .a file,  the link fials because it can't find _ZN3MPI2Op4InitEPFvPKvPviRKNS_8DatatypeEEb which c++filt demangles to:  

MPI::Op::Init(void (*)(void const*, void*, int, MPI::Datatype const&), bool)

The C version of this entry point is:  MPI_Op_Create

And, indeed in the old .so file (which I can link), there is a reference to MPI_Op_Create and no reference to ZN3MPI2Op4InitEPFvPKvPviRKNS_8DatatypeEEb whereas in the new .so file (which I cannot link),
there is a reference to _ZN3MPI2Op4InitEPFvPKvPviRKNS_8DatatypeEEb but none to MPI_Op_Create.

Unfortunately, I can't recreate the old .so file, so I have to work from the new one.  

The .a file from which the .so files are built contains references to both _ZN3MPI2Op4InitEPFvPKvPviRKNS_8DatatypeEEb and MPI_Op_Create.  (The two .so files are built from different versions of those .a files, but all versions of the .a files contain references to both entry points).

What might have changed to cause the new .so file to reference _ZN3MPI2Op4InitEPFvPKvPviRKNS_8DatatypeEEb instead of MPI_Op_Create.  

Thanks,
  Ken







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Question by:klopter
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>>>> What might have changed to cause the new .so file to reference
>>>>_ZN3MPI2Op4InitEPFvPKvPviRKNS_8DatatypeEEb instead of MPI_Op_Create.  

You need to switch off C++ name mangling when the function was declared. Normally you do that in the header file:

#ifdef __cplusplus
extern "C"
{
#endif

typedef struct OpTag
{
     void Init(void (*)(void const*, void*, int, MPI::Datatype const&), bool);
} Op;

#ifdef __cplusplus
}
#endif


You also could try to  put the extern "C" around the include of the header file where the Init function was defined.

// some.cpp

extern "C"
{
    #include <op.h>
}

Regards, Alex
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