---
name: "MPIL_Type_id"
section: "3"
platform: "linux"
package: "lam-mpidoc"
version: "7.1.4-7.2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/MPIL_Type_id/3"
---

# MPIL\_Type\_id(3)

LAM/MPI-specific function to return the type ID of an MPI datatype

## NAME

MPIL\_Type\_id -  LAM/MPI-specific function to return the type ID of an MPI datatype

## SYNOPSIS

```
#include <mpi.h>
int MPIL_Type_id(MPI_Datatype dtype, int *ptid)
```

## INPUT PARAMETER

- **dtype**

  \- MPI datatype (handle)

## OUTPUT PARAMETER

- **ptid**

  \- datatype ID (integer)

## NOTES

In the LAM implementation of MPI, each communicator has an integer context ID associated with it for synchronizing on different contexts. This ID is global to all the processes in the communicator's group, and uniquely identifies that communicator for each process.  These properties allow the processes to safely exchange messages without interference from operations on other communicators.

The MPI standard does not provide a way to access/view this implementation-dependent synchronization since communicators are opaque objects.  Users do not need such access for normal MPI operations.  On the other hand, when debugging MPI applications, the opaque nature of communicators hinders the user's efforts.  This is especially true on fully observable systems such as LAM, where users can monitor the full state of the processes and message queues, which includes the context ID (see  *mpitask* (1) and  *mpimsg* (1)).

This is a LAM/MPI-specific function and is intended mainly for debugging.  If this function is used, it should be used in conjunction with the  *LAM\_MPI* C preprocessor macro

```
#if LAM_MPI
int tid
MPIL_Type_id(MPI_INT, &tid);
#endif
```

## NOTES FOR FORTRAN

All MPI routines in Fortran (except for  *MPI\_WTIME* and  *MPI\_WTICK* ) have an additional argument  *ierr* at the end of the argument list. *ierr* 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  *call* statement.

All MPI objects (e.g.,  *MPI\_Datatype* ,  *MPI\_Comm* ) are of type *INTEGER* in Fortran.

## ERRORS

If an error occurs in an MPI function, the current MPI error handler is called to handle it.  By default, this error handler aborts the MPI job.  The error handler may be changed with  *MPI\_Errhandler\_set* ; the predefined error handler  *MPI\_ERRORS\_RETURN* may be used to cause error values to be returned (in C and Fortran; this error handler is less useful in with the C++ MPI bindings.  The predefined error handler  *MPI::ERRORS\_THROW\_EXCEPTIONS* should be used in C++ if the error value needs to be recovered).  Note that MPI does  *not* guarantee that an MPI program can continue past an error.

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 last argument.  The C++ bindings for MPI do not return error values; instead, error values are communicated by throwing exceptions of type  *MPI::Exception* (but not by default).  Exceptions are only thrown if the error value is not  *MPI::SUCCESS* .

Note that if the  *MPI::ERRORS\_RETURN* handler is set in C++, while MPI functions will return upon an error, there will be no way to recover what the actual error value was.

- **MPI\_SUCCESS**

  \- No error; MPI routine completed successfully.

- **MPI\_ERR\_TYPE**

  \- Invalid datatype argument.  May be an uncommitted MPI\_Datatype (see  *MPI\_Type\_commit* ).

- **MPI\_ERR\_ARG**

  \- Invalid argument.  Some argument is invalid and is not identified by a specific error class.  This is typically a NULL pointer or other such error.

## SEE ALSO

MPIL\_Comm\_gps, MPIL\_Comm\_id\

## LOCATION

mpil\_id.c