There is one blocking SEND routine for each of the four communication modes.

Regardless of communication mode, the send commands share the same syntax. In this section we'll take a quick look at the signature for these commands and review what the parameters mean. For a more in depth look, please refer to the MPI messages topic.

C:

int MPI_Send(void *buf, int count, MPI_Datatype datatype,
     int dest, int tag, MPI_Comm comm)
int MPI_Recv(void *buf, int count, MPI_Datatype datatype,
     int source, int tag, MPI_Comm comm, MPI_Status *status)

Fortran:

MPI_SEND(buf, count, datatype, dest, tag, comm, ierror)
MPI_RECV(buf, count, datatype, source, tag, comm, status, ierror)

Functional description of MPI_Send and Recv parameters.

buf

The beginning of the buffer containing the data to be sent. For Fortran, this is often the name of an array in your program. For C, it is an address.

count

The number of elements to be sent (not bytes).

datatype

The type of data, either a predefined MPI_Datatype or user-defined derivative type.

dest or source

The beginning of the buffer containing the data to be sent. For Fortran, this is often the name of an array in your program. For C, it is an address.

tag

The beginning of the buffer containing the data to be sent. For Fortran, this is often the name of an array in your program. For C, it is an address.

comm

The communicator id

ierror

The returned error code (Fortran only—in C, check the function's return value)

status

The array or structure of information that is returned. For example, if you specify a wildcard for source or tag, the status will tell you the actual rank or tag for the message received.