The Great and Terrible implementation of MPI-2

function index


Initialize the MPI execution environment
int MPI_Init(
  int *argc,
  char ***argv

int MPI_Init(
  int *argc,
  wchar_t ***argv


[in] Pointer to the number of arguments
[in] Pointer to the argument vector


This routine must be called before any other MPI routine. It must be called at most once; subsequent calls are erroneous (see MPI_INITIALIZED).

The MPI standard does not say what a program can do before an MPI_INIT or after an MPI_FINALIZE. In the MPICH implementation, you 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.

Thread and Signal Safety

This routine must be called by one thread only. That thread is called the main thread and must be the thread that calls MPI_Finalize.

Notes for Fortran

The Fortran binding for MPI_Init has only the error return
    subroutine MPI_INIT( ierr )
    integer ierr


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

No error; MPI routine completed successfully.
This error class is associated with an error code that indicates that an attempt was made to call MPI_INIT a second time. MPI_INIT may only be called once in a program.

See Also

MPI_Init_thread, MPI_Finalize

Example Code

The following sample code illustrates MPI_Init.

#include "mpi.h"
#include <stdio.h>
int main(int argc, char *argv[])
    int rank, nprocs;

    printf("Hello, world.  I am %d of %d\n", rank, nprocs);fflush(stdout);
return 0;