358. Fortran Support Through the mpif.h Include File

The use of the mpif.h include file is strongly discouraged and may be deprecated in a future version of MPI.

An MPI implementation providing a Fortran interface must provide an include file named mpif.h that can be used in a Fortran program. Within all MPI function specifications, the second of the set of two Fortran routine interface specifications is supported by this include file. This include file must:

• Define all named MPI constants.
• Declare MPI functions that return a value.
• Define all handles as INTEGER.
• Be valid and equivalent for both fixed and free source form.

• Set the LOGICAL compile-time constants MPI_SUBARRAYS_SUPPORTED and MPI_ASYNC_PROTECTS_NONBLOCKING according to the same rules as for the mpi module. In the case of implicit interfaces for choice buffer or nonblocking routines, the constants must be set to .FALSE..

Instead of using mpif.h, the use of the mpi_f08 or mpi module is strongly encouraged for the following reasons:

• Most mpif.h implementations do not include compile-time argument checking.
• Therefore, many bugs in MPI applications remain undetected at compile-time, such as:
  • Missing ierror as last argument in most Fortran bindings.
  • Declaration of a status as an INTEGER variable instead of an INTEGER array with size MPI_STATUS_SIZE.
  • Incorrect argument positions; e.g., interchanging the count and datatype arguments.
  • Passing incorrect MPI handles; e.g., passing a datatype instead of a communicator.

  
  
• The migration from mpif.h to the mpi module should be relatively straightforward (i.e., substituting include 'mpif.h' after an implicit statement by use mpi before that implicit statement) as long as the application syntax is correct.
• Migrating portable and correctly written applications to the mpi module is not expected to be difficult. No compile or runtime problems should occur because an mpif.h include file was always allowed to provide explicit Fortran interfaces.

With MPI-3.0, the mpif.h include file was not deprecated in order to retain strong backward compatibility. Internally, mpif.h and the mpi module may be implemented so that essentialy the same library implementation of the MPI routines can be used. ( End of rationale.)