---
name: "MPI_Type_create_keyval"
section: "3"
platform: "linux"
package: "openmpi"
version: "5.0.11-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/MPI_Type_create_keyval"
---

# MPI\_Type\_create\_keyval(3)

*MPI\_Type\_create\_keyval* — Generates a new attribute key for caching on data types.

## SYNTAX

### C Syntax

```
#include <mpi.h>
int MPI_Type_create_keyval(MPI_Type_copy_attr_function *type_copy_attr_fn,
     MPI_Type_delete_attr_function *type_delete_attr_fn,
     int *type_keyval, void *extra_state)
```

### Fortran Syntax

```
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TYPE_CREATE_KEYVAL(TYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN,
             TYPE_KEYVAL, EXTRA_STATE, IERROR)
     EXTERNAL TYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN
     INTEGER TYPE_KEYVAL, IERROR
     INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE
```

### Fortran 2008 Syntax

```
USE mpi_f08
MPI_Type_create_keyval(type_copy_attr_fn, type_delete_attr_fn, type_keyval,
             extra_state, ierror)
     PROCEDURE(MPI_Type_copy_attr_function) :: type_copy_attr_fn
     PROCEDURE(MPI_Type_delete_attr_function) :: type_delete_attr_fn
     INTEGER, INTENT(OUT) :: type_keyval
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: extra_state
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

## INPUT PARAMETERS

- •

  **type\_copy\_attr\_fn**: Copy callback function for *type\_keyval* (function).

- •

  **type\_delete\_attr\_fn**: Delete callback function for *type\_keyval* (function).

- •

  **extra\_state**: Extra state for callback functions.

## OUTPUT PARAMETERS

- •

  **type\_keyval**: Key value for future access (integer).

- •

  **ierror**: Fortran only: Error status (integer).

## DESCRIPTION

*MPI\_Type\_create\_keyval* generates a new attribute key for caching on data types. This routine partially replaces *MPI\_Keyval\_create*.

The argument *type\_copy\_attr\_fn* may be specified as MPI\_TYPE\_NULL\_COPY\_FN or MPI\_TYPE\_DUP\_FN from C or Fortran. MPI\_TYPE\_NULL\_COPY\_FN is a function that does nothing other than returning *flag* = 0 and MPI\_SUCCESS. MPI\_TYPE\_DUP\_FN is a simple-minded copy function that sets *flag* = 1, returns the value of *attribute\_val\_in* in *attribute\_val\_out*, and returns MPI\_SUCCESS.

The argument *type\_delete\_attr\_fn* may be specified as MPI\_TYPE\_NULL\_DELETE\_FN from C or Fortran. MPI\_TYPE\_NULL\_DELETE\_FN is a function that does nothing beyond returning MPI\_SUCCESS. The C callback functions are:

```
typedef int MPI_Type_copy_attr_function(MPI_Datatype oldtype,
            int type_keyval, void *extra_state, void *attribute_val_in,
            void *attribute_val_out, int *flag);
typedef int MPI_Type_delete_attr_function(MPI_Datatype type, int type_keyval,
             void *attribute_val, void *extra_state);
```

The Fortran callback functions are:

```
SUBROUTINE TYPE_COPY_ATTR_FN(OLDTYPE, TYPE_KEYVAL, EXTRA_STATE,
             ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, FLAG, IERROR)
    INTEGER OLDTYPE, TYPE KEYVAL, IERROR
    INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE,
        ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT
    LOGICAL FLAG
SUBROUTINE TYPE_DELETE_ATTR_FN(TYPE, TYPE_KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE,
             IERROR)
    INTEGER TYPE, TYPE_KEYVAL, IERROR
    INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE VAL, EXTRA_STATE
```

## 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.

**SEE ALSO:**

- •

  *MPI\_Type\_free\_keyval*

## COPYRIGHT

2003-2026, The Open MPI Community