MPI\_ALLOC\_MEM(3) Open MPI MPI\_ALLOC\_MEM(3)

MPI\_Alloc\_mem — Allocates a specified memory segment.

# [SYNTAX](#SYNTAX)

## [C Syntax](#C_Syntax)

```
#include <mpi.h>
int MPI_Alloc_mem(MPI_Aint size, MPI_Info info, void *baseptr)
```

## [Fortran Syntax](#Fortran_Syntax)

```
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_ALLOC_MEM(SIZE, INFO, BASEPTR, IERROR)


     INTEGER INFO, IERROR


     INTEGER(KIND=MPI_ADDRESS_KIND) SIZE, BASEPTR
```

## [Fortran 2008 Syntax](#Fortran_2008_Syntax)

```
USE mpi_f08
MPI_Alloc_mem(size, info, baseptr, ierror)


     USE, INTRINSIC :: ISO_C_BINDING, ONLY


     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: size


     TYPE(MPI_Info), INTENT(IN) :: info


     TYPE(C_PTR), INTENT(OUT) :: baseptr


     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

# [INPUT PARAMETERS](#INPUT_PARAMETERS)

- **size**: Size of memory segment in bytes (nonnegative integer).
- **info**: Info argument (handle).

# [OUTPUT PARAMETERS](#OUTPUT_PARAMETERS)

- **baseptr**: Pointer to beginning of memory segment allocated.
- **ierror**: Fortran only: Error status (integer).

# [DESCRIPTION](#DESCRIPTION)

MPI\_Alloc\_mem allocates *size* bytes of memory. The starting address of this memory is returned in the variable *baseptr*.

# [C NOTES](#C_NOTES)

The parameter *baseptr* is of type **void \*** to allow passing any pointer object for this parameter. The provided argument should be a pointer to a pointer of arbitrary type (e.g., **void \*\***).

# [FORTRAN NOTES](#FORTRAN_NOTES)

The MPI\_Alloc\_mem calls require the use of the **iso\_c\_binding** module for due to the use of **TYPE(C\_PTR)**.

```
use iso_c_binding
type(c_ptr) :: alloc_ptr
integer :: size, ierr
double precision, pointer :: array(:,:)
! A 2D array of 100 elements
size = 10 * 10
call MPI_Alloc_Mem(size * 8, MPI_INFO_NULL, alloc_ptr, ierr)
! Point to the array
call c_f_pointer(alloc_ptr, array, [10, 10])
! ... use the array ...
! Free the memory, no need for the alloc_ptr
call MPI_Free_mem(array, ierr)
```

# [ERRORS](#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 &lt;#mpi-init&gt;/MPI\_Init\_thread &lt;#mpi-init-thread&gt;, after MPI\_Finalize &lt;#mpi-finalize&gt;, 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 &lt;#mpi-comm-set-errhandler&gt; 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 &lt;#mpi-comm-spawn&gt;/MPI\_Comm\_spawn\_multiple &lt;#mpi-comm-spawn-multiple&gt;. 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 &lt;#mpi-abort&gt; was called on that communicator. If called on a window or file, acts as if MPI\_Abort &lt;#mpi-abort&gt; 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 &lt;#mpi-comm-create-errhandler&gt; then MPI\_Comm\_set\_errhandler &lt;#mpi-comm-set-errhandler&gt;
- MPI\_File\_create\_errhandler &lt;#mpi-file-create-errhandler&gt; then MPI\_File\_set\_errhandler &lt;#mpi-file-set-errhandler&gt;
- MPI\_Session\_create\_errhandler &lt;#mpi-session-create-errhandler&gt; then MPI\_Session\_set\_errhandler &lt;#mpi-session-set-errhandler&gt; or at MPI\_Session\_init &lt;#mpi-session-init&gt;
- MPI\_Win\_create\_errhandler &lt;#mpi-win-create-errhandler&gt; then MPI\_Win\_set\_errhandler &lt;#mpi-win-set-errhandler&gt;

Note that MPI does not guarantee that an MPI program can continue past an error.

See the MPI man page &lt;#open-mpi&gt; for a full list of MPI error codes &lt;#open-mpi-errors&gt;.

See the Error Handling section of the MPI-3.1 standard for more information.

**See also:**

•

MPI\_Free\_mem &lt;#mpi-free-mem&gt;

# [Copyright](#Copyright)

2003-2026, The Open MPI Community

September 23, 2026

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Document: MPI_Alloc_mem(3) from openmpi-cuda-12.9 5.0.11-r0 (Chainguard OS)
Source: https://github.com/open-mpi/ompi