Bill Long wrote:

...

There isn't any difficulty about a Fortran wrapper using integers (as C does), and converting them to LOGICAL, but it can't be BIND(C).

There is also no difficulty in having the wrapper arguments being LOGICAL.

subroutine sub (x) bind(c, name="MPI_xxx_f") logical :: x integer(int) :: cx

cx = merge(1, 0, x)

Well, except that compilers might simply reject a default-kind LOGICAL with BIND(C), in line with the Fortran standard. Your code above assumes that a Fortran compiler allows passing a default-kind LOGICAL to a Bind(C) procedure and that it then can handle that LOGICAL. I think no one really doubts the second part. But the first part is not really covered by the Fortran standard and standard-conforming compilers do exist, which reject default-kind LOGICALs. J3/WG5 could change the standard such that it supports other LOGICAL kinds besides C_Bool, including kind(.true.). However, if LOGICAL(kind=kind(.true.) / C_INT) exists, users will assume that it acts like C's "int", which will lead to problems. So far, I haven't seen a convincing proposal how to solve this. Tobias