The following two procedures are provided in C to convert from a
Fortran status (which is an array of integers) to a C status (which is
a structure), and vice versa.
The conversion occurs on all the information in status, including that which
is hidden. That is, no status information is lost in the conversion.
int MPI_Status_f2c(MPI_Fint *f_status, MPI_Status *c_status)
If f_status is a valid Fortran status, but not the Fortran value of MPI_STATUS_IGNORE or MPI_STATUSES_IGNORE, then MPI_Status_f2c returns in c_status a valid C status with the same content. If f_status is the Fortran value of MPI_STATUS_IGNORE or MPI_STATUSES_IGNORE, or if f_status is not a valid Fortran status, then the call is erroneous.
The C status has the same source, tag and error code values as the Fortran status, and returns the same answers when queried for count, elements, and cancellation. The conversion function may be called with a Fortran status argument that has an undefined error field, in which case the value of the error field in the C status argument is undefined.
Two global variables of type MPI_Fint*, MPI_F_STATUS_IGNORE and MPI_F_STATUSES_IGNORE are declared in mpi.h. They can be used to test, in C, whether f_status is the Fortran value of MPI_STATUS_IGNORE or MPI_STATUSES_IGNORE, respectively. These are global variables, not C constant expressions and cannot be used in places where C requires constant expressions. Their value is defined only between the calls to MPI_INIT and MPI_FINALIZE and should not be changed by user code.
To do the conversion in the other direction, we have the following:
int MPI_Status_c2f(MPI_Status *c_status, MPI_Fint *f_status)
This call converts a C status into a Fortran status, and has a behavior similar to MPI_Status_f2c. That is, the value of c_status must not be either MPI_STATUS_IGNORE or MPI_STATUSES_IGNORE.
Advice to users.
There is not a separate conversion function for arrays of statuses, since one
can simply loop through the array, converting each status.
( End of advice to users.)
Rationale.
The handling of MPI_STATUS_IGNORE is required in order to
layer libraries with only a C wrapper: if the Fortran call has passed
MPI_STATUS_IGNORE, then the C wrapper must handle this
correctly.
Note that this constant need not have the same value in
Fortran and C. If MPI_Status_f2c were to handle
MPI_STATUS_IGNORE, then the type of its result would have to be
MPI_Status**, which was considered an inferior solution.
( End of rationale.)