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Table of Contents
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1. Language
.. 1. Is there an equivalent of _Static_assert(sizeof(struct my_struct) = 48)?
.. 2. How do I check for trailing bytes at the end of a file





1 Language
==========

1.1 Is there an equivalent of _Static_assert(sizeof(struct my_struct) = 48)?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  If the struct type My_Struct is complete, i.e. its size can be
  determined at compile-time, then you can do this:

  ,----
  | assert (1#My_Struct == 48#B)
  `----


  Otherwise you can construct a struct value and use the 'size attribute
  like this:

  ,----
  | assert (My_Struct{}'size == 48#B)
  `----


1.2 How do I check for trailing bytes at the end of a file
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  When you have a single mapping that (supposedly) wholly encompasses a
  file, it may be useful to be able to deal with extraneous bytes at the
  end: then iosize(fd) comes in handy:

  ,----
  | var fd = open("/etc/passwd");
  | type mytype = char[200];
  | var relevant = mytype @ fd : 0#B;
  | var trailing_len = iosize(fd) - relevant'size;
  `----


  One way to deal with it would be to assert that it doesn't happen:
  ,----
  | assert(0#B == trailing_len); // or simply:
  | assert(iosize(fd) == relevant'size);
  `----


  Or you can carve it out and parade it:
  ,----
  | var trailing_chars = char[] @ fd : iosize(fd) - trailing_len;
  | var trim = alignto(trailing_len, sizeof(short));
  | var trailing_shorts = short[trailing_len - trim] @ fd : relevant'size;
  | assert(relevant'size + trailing_shorts'size + trim == iosize(fd));
  | assert(trim'magnitude*trim'unit == iosize(fd)/#b % 16);
  `----