Retrieves attribute value by key


#include "mpi.h"
int MPI_Attr_get ( comm, keyval, attr_value, flag )
MPI_Comm comm;
int keyval;
void *attr_value;
int *flag;

Input Parameters

comm communicator to which attribute is attached (handle)
keyval key value (integer)

Output Parameters

attr_value attribute value, unless flag = false
flag true if an attribute value was extracted; false if no attribute is associated with the key


Attributes must be extracted from the same language as they were insertedin with MPI_ATTR_PUT. The notes for C and Fortran below explain why.

Notes for C

Even though the attr_value arguement is declared as void *, it isreally the address of a void pointer. See the rationale in thestandard for more details.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) havean additional argument ierr at the end of the argument list. ierris an integer and has the same meaning as the return value of the routinein C. In Fortran, MPI routines are subroutines, and are invoked with thecall statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGERin Fortran.

The attr_value in Fortran is a pointer to a Fortran integer, nota pointer to a void *.


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 lastargument. Before the value is returned, the current MPI error handler iscalled. By default, this error handler aborts the MPI job. The error handlermay be changed with MPI_Errhandler_set; the predefined error handlerMPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue pastan error.

No error; MPI routine completed successfully.
Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).
Other error; the error code associated with this error indicates an attempt to use an invalue keyval.