Routines (alphabetical) > Routines: G > GET_LUN

# GET_LUN

The GET_LUN procedure allocates a file unit from a pool of free units. Instead of writing routines to assume the use of certain file units, IDL functions and procedures should use GET_LUN to reserve unit numbers in order to avoid conflicts with other routines. Use FREE_LUN to free the file units when finished.

## Examples

Instead of explicitly specifying a file unit number that may already be used, use GET_LUN to obtain a free one and store the result in the variable U by entering:

GET_LUN, U

Now U can be used in opening a file:

OPENR, U, 'file.dat'

Once the data from “file.dat” has been read, the file can be closed and the file unit can be freed with the command:

FREE_LUN, U

Note also that OPENR has a GET_LUN keyword that allows you to simultaneously obtain a free file unit and open a file. The following command performs the same tasks as the first two commands above:

OPENR, U, 'file.dat', /GET_LUN

## Syntax

GET_LUN, Unit

## Arguments

### Unit

The named variable into which GET_LUN should place the file unit number. Unit is converted into a longword integer in the process. The file unit number obtained is in the range 100 to 128.

## Keywords

None.

## Version History

Original | Introduced

## See Also

FREE_LUN, OPENR/OPENU/OPENW, Understanding (LUNs)