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  Arguments
 
    filename    Untyped file; source of copying procedure
 
    buffer      Any variable; destination of copying procedure
 
    count       Integer expression; number of blocks to be copied
 
    result      Optional; number of complete blocks copied
 
  Description
 
    The BlockRead procedure copies one or more blocks from an untyped
    file to a user-defined buffer. Before using BlockRead, Assign the
    file, then Reset the file. After BlockRead, the current position in
    the file advances the number of blocks given by result.
 
    BlockRead copies data in blocks of size specified when the file was
    opened with the Reset procedure. If no size was specified,
    BlockRead uses a default size of 128 bytes. The block size may be
    specified to match the size of records stored in the file, as long
    as the size is less than 64K.
 
    Beginning at the first byte of the buffer, BlockRead fills as much
    memory as needed. Since BlockRead does not perform range-checking,
    make sure that the buffer size in bytes equals or exceeds the
    product of count and the block size.
 
    If the result argument is passed, BlockRead sets result to the
    number of complete blocks copied, excluding any last partial
    block. If the file size is not a multiple of the block size, a
    partial record remains unread in the file.
 
    If result is not passed and the number of complete blocks copied is
    less than count, an I/O error occurs.
 
    To prevent a program from halting with a run-time error when an I/O
    error occurs, turn off I/O checking with {$I-} and check the return
    value of the IOResult function.