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SYNTAX
C Syntax
#include <mpi.h>
int MPI_Bcast(void *buffer, int count, MPI_Datatype datatype,
int root, MPI_Comm comm)
int MPI_Ibcast(void *buffer, int count, MPI_Datatype datatype,
int root, MPI_Comm comm, MPI_Request *request)
Fortran Syntax
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_BCAST(BUFFER, COUNT, DATATYPE, ROOT, COMM, IERROR)
<type> BUFFER(*)
INTEGER COUNT, DATATYPE, ROOT, COMM, IERROR
MPI_IBCAST(BUFFER, COUNT, DATATYPE, ROOT, COMM, REQUEST, IERROR)
<type> BUFFER(*)
INTEGER COUNT, DATATYPE, ROOT, COMM, REQUEST, IERROR
Fortran 2008 Syntax
USE mpi_f08
MPI_Bcast(buffer, count, datatype, root, comm, ierror)
TYPE(*), DIMENSION(..) :: buffer
INTEGER, INTENT(IN) :: count, root
TYPE(MPI_Datatype), INTENT(IN) :: datatype
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_Ibcast(buffer, count, datatype, root, comm, request, ierror)
TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buffer
INTEGER, INTENT(IN) :: count, root
TYPE(MPI_Datatype), INTENT(IN) :: datatype
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Request), INTENT(OUT) :: request
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
INPUT/OUTPUT PARAMETERS
• buffer: Starting address of buffer (choice).
• count: Number of entries in buffer (integer).
• datatype: Data type of buffer (handle).
• root: Rank of broadcast root (integer).
• comm: Communicator (handle).
OUTPUT PARAMETERS
• request: Request (handle, non-blocking only).
• ierror: Fortran only: Error status (integer).
DESCRIPTION
MPI_Bcast broadcasts a message from the process with rank root to all processes of the group, itself
included. It is called by all members of group using the same arguments for comm, root. On return, the
contents of root’s communication buffer has been copied to all processes.
General, derived datatypes are allowed for datatype. The type signature of count, datatype on any process
must be equal to the type signature o f count, datatype at the root. This implies that the amount of data
sent must be equal to the amount received, pairwise between each process and the root. MPI_Bcast and all
other data-movement collective routines make this restriction. Distinct type maps between sender and
receiver are still allowed.
Example: Broadcast 100 ints from process 0 to every process in the group.
MPI_Comm comm;
int array[100];
int root=0;
//...
MPI_Bcast( array, 100, MPI_INT, root, comm);
As in many of our sample code fragments, we assume that some of the variables (such as comm in the
example above) have been assigned appropriate values.
WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR
When the communicator is an inter-communicator, the root process in the first group broadcasts data to
all the processes in the second group. The first group defines the root process. That process uses
MPI_ROOT as the value of its root argument. The remaining processes use MPI_PROC_NULL as the value of
their root argument. All processes in the second group use the rank of that root process in the first
group as the value of their root argument. The receive buffer arguments of the processes in the second
group must be consistent with the send buffer argument of the root process in the first group.
NOTES
This function does not support the in-place option.
ERRORS
Almost all MPI routines return an error value; C routines as the return result of the function and
Fortran routines in the last argument.
Before the error value is returned, the current MPI error handler associated with the communication
object (e.g., communicator, window, file) is called. If no communication object is associated with the
MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error
handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after
MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler.
The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/‐
MPI_Comm_spawn_multiple. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all
other MPI functions.
Open MPI includes three predefined error handlers that can be used:
• MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.
• MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a
window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in
the corresponding window or file. If called on a session, aborts only the local process.
• MPI_ERRORS_RETURN Returns an error code to the application.
MPI applications can also implement their own error handlers by calling:
• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler
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.
See the Error Handling section of the MPI-3.1 standard for more information.
COPYRIGHT
2003-2025, The Open MPI Community
Feb 17, 2025 MPI_BCAST(3)