MPI_Aint is always signed, as it is supposed to be able to hold any relative difference between two memory locations. This it is a good match for ptrdiff_t.
There is no direct match for size_t, at least not directly exposed by the MPI standard (using the MPI-2.2 POSIX types, e.g MPI_UINT64_T). My understanding is that size_t is unsigned, and ssize_t is the signed synonym. George. On Mar 13, 2013, at 23:30 , Gus Correa <g...@ldeo.columbia.edu> wrote: > Dear Open MPI Pros > > Which MPI data type corresponds to ptrdiff_t in C? > I guess the same question can be asked about size_t. > > The FFTW3.3 MPI API has lots of stuff declared as > ptrdiff_t, and I need to pass them around with MPI, > hopefully without size or sign mistakes. > > I am using Open MPI 1.6.3, if this matters. > My C goes as far as ABC, and in my naive view > ptrdiff_t is signed and has 64-bits on my x86_64 Linux computer, > whereas size_t is unsigned also 64-bits, right? > > If I grep mpi.h for ptrdiff I see that OPAL_PTRDIFF_TYPE is > MPI_Aint, which is indeed an MPI pointer/address type. > However, this is OPAL, not generic MPI. > Moreover, MPI_Aint seems to be unsigned, right? > [And this would make it a bad match for ptrdiff_t, > but maybe a good match for size_t.] > Or is MPI_Aint signed? > > [grep result:] > 147:/* type to use for ptrdiff_t, if it does not exist, set to ptrdiff_t if > it does exist */ > 148:#define OPAL_PTRDIFF_TYPE ptrdiff_t > 218:/* include for ptrdiff_t */ > 317:typedef OPAL_PTRDIFF_TYPE MPI_Aint; > > OTOH, there are bunches of signed and unsigned integer MPI types > in mpi.h. > In a 64-bit machine, besides MPI_Aint, > I guess possible candidates would be > MPI_INT64_T and MPI_UINT64_T. > But which one: signed or unsigned? > > Even if I write a little function to find an MPI integer type > with the same extent as sizeof(ptrdiff_t), it may still > return more than one type, and be problematic to pick one > (e.g., signed or unsigned?). > > Any help is appreciated. > Gus Correa > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users
