MPI_Init(3) Open MPI MPI_Init(3)

MPI_Init - Initializes the MPI execution environment

#include <mpi.h>
int MPI_Init(int *argc, char ***argv)

! or the older form: INCLUDE 'mpif.h'

USE mpi_f08

#include <mpi.h>
void MPI::Init(int& argc, char**& argv)
void MPI::Init()

C/C++ only: Pointer to the number of arguments.
C/C++ only: Argument vector.

Fortran only: Error status (integer).

This routine, or MPI_Init_thread, must be called before most other MPI routines are called. There are a small number of exceptions, such as MPI_Initialized and MPI_Finalized. MPI can be initialized at most once; subsequent calls to MPI_Init or MPI_Init_thread are erroneous.

All MPI programs must contain a call to MPI_Init or MPI_Init_thread. Open MPI accepts the C/C++ argc and argv arguments to main, but neither modifies, interprets, nor distributes them:

	/* declare variables */
	MPI_Init(&argc, &argv);
	/* parse arguments */
	/* main program */

The Fortran version does not have provisions for argc and argv and takes only IERROR.

The MPI Standard does not say what a program can do before an MPI_Init or after an MPI_Finalize. In the Open MPI implementation, it should do as little as possible. In particular, avoid anything that changes the external state of the program, such as opening files, reading standard input, or writing to standard output.

Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.

Before the error value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

See the MPI man page for a full list of MPI error codes.

May 26, 2022 4.1.4