[gmx-developers] Using C++ with Gromacs

[Yang Ye]

Hi, Peter

I am not sure what level of integration you desires with OpenMM.
You shall be able to write a wrapper for libgmx or libmd, built separately.
Any more information about what are needed for the wrapper, the 
so-called API to OpenMM?

Regards,
Yang Ye

Peter Eastman wrote:
> Hi,
>
> I'm working on trying to add OpenMM support to Gromacs (see 
> https://simtk.org/home/openmm).  I'm running into a variety of 
> problems that I hope someone can help me with.
>
> I'm trying to add a single source file to Gromacs which will take care 
> of all the interaction between it and OpenMM.  Since OpenMM is written 
> in C++, the file must use C++.  I've called it md_openmm.cpp.
>
> In theory, this should be simple.  I added the line
>
> AC_PROG_CXX
>
> to configure.ac to enable C++ support.  Then in 
> src/kernel/Makefile.ac, I added md_openmm.cpp to mdrun_SOURCES.  When 
> I run make, however, it fails with the following error:
>
> make[3]: *** No rule to make target `md_openmm.c', needed by 
> `md_openmm.o'.  Stop.
>
> There is, of course, no such file as "md_openmm.c", nor is there any 
> mention of such a file anywhere.  But somehow it's concluding that it 
> wants to build md_openmm.o, and that the source file to build it from 
> *ought* to be called md_openmm.c.
>
> I also tried adding md_openmm.cpp to 
> libgmxpreprocess at LIBSUFFIX@_la_SOURCES instead of mdrun_SOURCES.  If I 
> do that, it successfully finds the file and compiles it.  But when I 
> have md.c try to call a function defined in that file, the linker 
> fails to find it.
>
> Any advice would be very much appreciated.
>
> I've also encountered a second problem.   simple.h contains the 
> following code:
>
> #ifndef HAVE_BOOL
> #define bool int
>   /* typedef int             bool; */
> #endif
>
> HAVE_BOOL is not defined, presumably because the "bool" type is not 
> supported in standard C.  But the presence of this #define causes all 
> sorts of compilation errors if any Gromacs headers are included in a 
> C++ source file.  I can sort of work around them by including the 
> Gromacs headers after all other header files, then being very careful 
> not to use the bool type anywhere.  But that's very fragile.  Also, 
> using a #define instead of a typedef means that *any* occurrence of 
> the characters "bool" will be replaced - as part of a function name, 
> inside a character string, etc.  This seems almost certain to produce 
> bugs at some point.  Would it make more sense to switch to using a new 
> type name (e.g. gmxbool), rather than redefining a standard type to 
> mean something else?
>
> Thanks for your help!
>
> Peter
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