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  Arguments
 
    filename    Untyped file; destination of copying procedure
 
    buffer      Any variable; source of copying procedure
 
    count       Integer expression; number of blocks to be copied
 
    result      Optional; number of complete blocks copied
 
  Description
 
    The BlockWrite procedure copies one or more blocks from a
    user-defined buffer to an untyped file. Before using BlockWrite,
    Assign the file, then Reset or Rewrite the file. After BlockWrite,
    the current position in the file advances the number of blocks
    given by result.
 
    BlockWrite copies data in blocks of size specified when the file
    was opened with the Reset or Rewrite procedures. If no size is
    specified, BlockWrite uses a default size of 128 bytes. The block
    size may be specified to match the size of records to be stored
    in the file as long as the size is less than 64K.
 
    Beginning at the first byte of the buffer, BlockWrite copies
    successive blocks to the file. Since BlockWrite 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, BlockWrite sets result to the
    number of complete blocks copied. The number of bytes copied is, at
    most, the product of count and the block size. The number of bytes
    copied must not exceed 64K. If the disk becomes full, BlockWrite
    sets result to the number of blocks actually written.
 
    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.