TRUNCATE_LUN

Syntax | Arguments | Keywords | Examples | Version History | See Also

The TRUNCATE_LUN procedure truncates the contents of a file (which must be open for write access) at the current position of the file pointer. After this operation, all data before the current file pointer remains intact, and all data following the file pointer are gone. The position of the current file pointer is not altered.

Syntax

TRUNCATE_LUN, Unit₁, ..., Unit_n

Arguments

Unit_n

Scalar or array variables containing the logical file unit numbers of the open files to be truncated.

Keywords

None.

Examples

Example 1

Truncate the entire contents of an existing file:

OPENU, unit, 'baddata.dat', /GET_LUN 
TRUNCATE_LUN, unit 
FREE_LUN, unit 

Example 2

Given an existing file of 10,000 bytes, throw away the final 5,000 bytes, and then write an additional 2,000 byte array in their place. The resulting file will be 7,000 bytes in length.

OPENU, unit, 'mydata.dat', /GET_LUN 
POINT_LUN, unit, 5000 
TRUNCATE_LUN, unit 
WRITEU, unit, BYTARR(2000) 
FREE_LUN, unit 

Version History

See Also

GET_LUN, OPENR/OPENU/OPENW, POINT_LUN