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<H1 id="MPI_Type_get_attr">MPI_Type_get_attr</H1>
Retrieves attribute value by key
<H2>Synopsis</H2>
<PRE>
int MPI_Type_get_attr(MPI_Datatype datatype, int type_keyval, void *attribute_val, int *flag)
</PRE>
<H2>Input Parameters</H2>
<DL>
<DT><B>datatype </B> <DD> datatype to which the attribute is attached (handle)
<DT><B>type_keyval </B> <DD> key value (integer)
</DL>
<P>
<H2>Output Parameters</H2>
<DL>
<DT><B>attribute_val </B> <DD> attribute value, unless flag = false
<DT><B>flag </B> <DD> false if no attribute is associated with the key (logical)
</DL>
<P>
<H2>Notes</H2>
Attributes must be extracted from the same language as they were inserted
in with <tt>MPI_Type_set_attr</tt>. The notes for C and Fortran below explain
why.
<P>
<H2>Notes for C</H2>
Even though the <tt>attr_value</tt> argument is declared as <tt>void *</tt>, it is
really the address of a void pointer. See the rationale in the
standard for more details.
<P>
<H2>Thread and Interrupt Safety</H2>
<P>
This routine is thread-safe. This means that this routine may be
safely used by multiple threads without the need for any user-provided
thread locks. However, the routine is not interrupt safe. Typically,
this is due to the use of memory allocation routines such as <tt>malloc
</tt>or other non-MPICH runtime routines that are themselves not interrupt-safe.
<P>
<H2>Notes for Fortran</H2>
All MPI routines in Fortran (except for <tt>MPI_WTIME</tt> and <tt>MPI_WTICK</tt>) have
an additional argument <tt>ierr</tt> at the end of the argument list. <tt>ierr
</tt>is an integer and has the same meaning as the return value of the routine
in C. In Fortran, MPI routines are subroutines, and are invoked with the
<tt>call</tt> statement.
<P>
All MPI objects (e.g., <tt>MPI_Datatype</tt>, <tt>MPI_Comm</tt>) are of type <tt>INTEGER
</tt>in Fortran.
<P>
<H2>Errors</H2>
<P>
All MPI routines (except <tt>MPI_Wtime</tt> and <tt>MPI_Wtick</tt>) 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 <tt>MPI_Comm_set_errhandler</tt> (for communicators),
<tt>MPI_File_set_errhandler</tt> (for files), and <tt>MPI_Win_set_errhandler</tt> (for
RMA windows). The MPI-1 routine <tt>MPI_Errhandler_set</tt> may be used but
its use is deprecated. The predefined error handler
<tt>MPI_ERRORS_RETURN</tt> may be used to cause error values to be returned.
Note that MPI does <em>not</em> guarentee that an MPI program can continue past
an error; however, MPI implementations will attempt to continue whenever
possible.
<P>
<DL>
<DT><B>MPI_SUCCESS </B> <DD> No error; MPI routine completed successfully.
</DL>
<DL>
<DT><B>MPI_ERR_KEYVAL </B> <DD> Invalid keyval
</DL>
<DL>
<DT><B>MPI_ERR_ARG </B> <DD> Invalid argument. Some argument is invalid and is not
identified by a specific error class (e.g., <tt>MPI_ERR_RANK</tt>).
</DL>
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