The truncate function changes the length of a file to the size,
    in bytes, specified by the length argument.

    If the new length is less than the previous length, the function
    removes all data beyond length bytes from the specified file. All
    file data between the new End-of-File and the previous End-of-
    File is discarded.

    For stream files, if the new length is greater than the previous
    length, new file data between the previous End-of-File and the
    new End-of-File is added, consisting of all zeros. (For record
    files, it is not possible to extend the file in this manner.)