# MPI_Init

Initialize the MPI execution environment

## Synopsis

    int MPI_Init(int *argc, char ***argv)

## Input Parameters

argc
  Pointer to the number of arguments
argv
  Pointer to the argument vector

## 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

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.

## Notes for C

As of MPI-2, `MPI_Init` will accept NULL as input parameters. Doing so will impact the values stored in `MPI_INFO_ENV`.

## Notes for Fortran

The Fortran binding for `MPI_Init` has only the error return

        subroutine MPI_INIT(ierr)
        integer ierr

## Errors

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 guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS
  No error; MPI routine completed successfully.

MPI_ERR_OTHER
  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