---
name: "MPI_T_cvar_get_info"
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_T_cvar_get_info"
---

# MPI\_T\_cvar\_get\_info(3)

MPI\_T see MPI-3 section 14.3.5.

*MPI\_T\_cvar\_get\_info* — Query information from a control variable

## SYNTAX

### C Syntax

```
#include <mpi.h>
int MPI_T_cvar_get_info(int cvar_index, char *name, int *name_len,
                        int *verbosity, MPI_Datatype *datatype, MPI_T_enum *enumtype,
                        const *desc, int *desc_len, int *bind, int *scope)
```

## INPUT PARAMETERS

- •

  **cvar\_index**: Index of the control variable to be queried.

## INPUT/OUTPUT PARAMETERS

- •

  **name\_len**: Length of the string and/or buffer for name.

- •

  **desc\_len**: Length of the string and/or buffer for desc.

## OUTPUT PARAMETERS

- •

  **name**: Buffer to return the string containing the name of the control variable.

- •

  **verbosity**: Verbosity level of this variable.

- •

  **datatype**: MPI datatype of the information stored in the control variable.

- •

  **enumtype**: Optional descriptor for enumeration information.

- •

  **desc**: Buffer to return the string containing the description of the control variable.

- •

  **bind**: Type of MPI object to which this variable must be bound.

- •

  **scope**: Scope of when changes to this variable are possible.

## DESCRIPTION

*MPI\_T\_cvar\_get\_info* can be used to query information about a control variable. The function returns the verbosity, datatype, enumeration type, binding, and scope of the queried control variable in the arguments *verbosity*, *datatype*, *enumtype*, *bind*, and *scope*, respectively. Control variables in Open MPI are the same as MCA parameters.

## VERBOSITY

As Open MPI exposes a very large number of MCA parameters (control variables), control variables are categorized into nine verbosity levels corresponding to the equivalent *ompi\_info* level. The nine levels are (in increasing order):

- 1\.

  **MPI\_T\_VERBOSITY\_USER\_BASIC**: Basic information of interest to users

- 2\.

  **MPI\_T\_VERBOSITY\_USER\_DETAIL**: Detailed information of interest to users

- 3\.

  **MPI\_T\_VERBOSITY\_USER\_ALL**: All remaining information of interest to users

- 4\.

  **MPI\_T\_VERBOSITY\_TUNER\_BASIC**: Basic information required for tuning

- 5\.

  **MPI\_T\_VERBOSITY\_TUNER\_DETAIL**: Detailed information required for tuning

- 6\.

  **MPI\_T\_VERBOSITY\_TUNER\_ALL**: All remaining information required for tuning

- 7\.

  **MPI\_T\_VERBOSITY\_MPIDEV\_BASIC**: Basic information for MPI implementors

- 8\.

  **MPI\_T\_VERBOSITY\_MPIDEV\_DETAIL**: Detailed information for MPI implementors

- 9\.

  **MPI\_T\_VERBOSITY\_MPIDEV\_ALL**: All remaining information for MPI implementors

For more information see MPI-3 section 14.3.1.

## DATATYPE

The datatype returned by *MPI\_T\_cvar\_get\_info* is restricted to one of the following datatypes: **MPI\_INT**, **MPI\_UNSIGNED**, **MPI\_UNSIGNED\_LONG**, **MPI\_UNSIGNED\_LONG\_LONG**, **MPI\_COUNT**, **MPI\_CHAR**, and **MPI\_DOUBLE**. For more information on datatypes in MPI\_T see MPI-3 section 14.3.5.

## SCOPE

The scope describes when and how changes can be made to a control variable. From MPI-3 section 14.3.6, the scope may be any of the following:

- •

  **MPI\_T\_SCOPE\_CONSTANT**: read-only, value is constant

- •

  **MPI\_T\_SCOPE\_READONLY**: read-only, cannot be written, but can change

- •

  **MPI\_T\_SCOPE\_LOCAL**: may be writeable, writing is a local operation

- •

  **MPI\_T\_SCOPE\_GROUP**: may be writeable, must be done to a group of processes, all processes in a group must be set to consistent values

- •

  **MPI\_T\_SCOPE\_GROUP\_EQ**: may be writeable, must be done to a group of processes, all processes in a group must be set to the same value

- •

  **MPI\_T\_SCOPE\_ALL**: may be writeable, must be done to all processes, all connected processes must be set to consistent values

- •

  **MPI\_T\_SCOPE\_ALL\_EQ**: may be writeable, must be done to all processes, all connected processes must be set to the same value

For more information see MPI-3 section 14.3.6 Table 14.4.

## NOTES

This MPI tool interface function returns two strings. This function takes two argument for each string: a buffer to store the string, and a length which must initially specify the size of the buffer. If the length passed is n then this function will copy at most n - 1 characters of the string into the corresponding buffer and set the length to the number of characters copied - 1. If the length argument is NULL or the value specified in the length is 0 the corresponding string buffer is ignored and the string is not returned.

Open MPI does not currently support binding control variables to MPI objects.

## ERRORS

*MPI\_T\_cvar\_get\_info* will fail if:

- •

  **MPI\_T\_ERR\_NOT\_INITIALIZED**: The MPI Tools interface not initialized

- •

  **MPI\_T\_ERR\_INVALID\_INDEX**: The control variable index is invalid

**SEE ALSO:**

*ompi\_info*

## COPYRIGHT

2003-2026, The Open MPI Community