fortran 90 user defined type, passing by value ?

Programmer Question

I have an issue in Fortran 90.

I have a user-defined type, and when I call one of the MPI subroutines the data looks to be passed by value (not address, as I thought it should). The output arguments aren't modified. It seems to be specific to the MPI calls. I tried the same thing in a simple test, and I can change the passed in values in the calling scope. I'm not sure why this is, because I thought Fortran always passes by address. Any idea what could be going on?

Just to be clear, the commented snippet shows how the calls are made. In the first call, c%NSubDomains is an output argument and should be modified in the calling scope, but is not. When I call with an array rather than a member of a user-defined type it works, in the uncommented snippet.

! ! This doesn't work output values aren't modified ??
! call MPI_Dims_create(c%NProcs,c%NDims,c%NSubDomains,iErr)

nsubs(:)=0
call MPI_Dims_create(c%NProcs,c%NDims,nsubs,iErr)
c%NSubDomains=nsubs

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