# Name

`MPI_Comm_delete_attr` - Deletes attribute value associated with a
key.

# Syntax

## C Syntax

```c
#include <mpi.h>

int MPI_Comm_delete_attr(MPI_Comm comm, int comm_keyval)
```

## Fortran Syntax

```fortran
USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_COMM_DELETE_ATTR(COMM, COMM_KEYVAL, IERROR)
    INTEGER	COMM, COMM_KEYVAL, IERROR 
```

## Fortran 2008 Syntax

```fortran
USE mpi_f08

MPI_Comm_delete_attr(comm, comm_keyval, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm
    INTEGER, INTENT(IN) :: comm_keyval
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

## Input/Output Parameter

* `comm` : Communicator from which the attribute is deleted (handle).

# Input Parameter

* `comm_keyval` : Key value (integer).

# Output Parameter

* `IERROR` : Fortran only: Error status (integer).

# Description

`MPI_Comm_delete_attr` deletes an attribute from cache by key. This
function invokes the attribute delete function `delete_fn` specified when
the `comm_keyval` was created. The call will fail if the `delete_fn`
function returns an error code other than `MPI_SUCCESS.`
Whenever a communicator is replicated using the function `MPI_Comm_dup`,
all callback copy functions for attributes that are currently set are
invoked (in arbitrary order). Whenever a communicator is deleted using
the function `MPI_Comm_free`, all callback delete functions for attributes
that are currently set are invoked.
This function is the same as `MPI_Attr_delete` but is needed to match the
`comm`unicator-specific functions introduced in the MPI-2 standard. The
use of `MPI_Attr_delete` is deprecated.

# Notes

Note that it is not defined by the MPI standard what happens if the
`delete_fn` callback invokes other MPI functions. In Open MPI, it is not
valid for `delete_fn` callbacks (or any of their children) to add or
delete attributes on the same object on which the `delete_fn` callback is
being invoked.

# Errors

Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument.
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
`MPI_Comm_set_errhandler`; 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.