7. How To Truncate A File

There is not any single DOS Int 21h function that performs this
operation.  A file can be truncated using two functions.  The procedure
is:

1.  Use Int 21h function 42h, Move File Pointer, to move the file
    pointer to the position where you want the file to be truncated.
2.  Use Int 21h function 40h, Write File or Device, to write zero bytes
    to the file.

Execution of the last DOS function will update the directory to the new
file length.

Contributor: Raymond Moon, raymoon@moonware.dgsys.com
Last changed: 28 Dec 94

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Last Update October 22 2009 @ 05:22 AM