ceph/src/boost/libs/mpl/doc/src/refmanual/sizeof_.rst

   1 .. Metafunctions/Miscellaneous//sizeof_ |100
   2
   3 sizeof\_
   4 ========
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename X
  13         >
  14     struct sizeof\_
  15     {
  16         typedef |unspecified| type;
  17     };
  18
  19
  20
  21 Description
  22 -----------
  23
  24 Returns the result of a ``sizeof(X)`` expression wrapped into an
  25 |Integral Constant| of the corresponding type, ``std::size_t``.
  26
  27
  28 Header
  29 ------
  30
  31 .. parsed-literal::
  32
  33     #include <boost/mpl/sizeof.hpp>
  34
  35
  36 Model of
  37 --------
  38
  39 |Metafunction|
  40
  41
  42 Parameters
  43 ----------
  44
  45 +---------------+-------------------+-------------------------------------------+
  46 | Parameter     | Requirement       | Description                               |
  47 +===============+===================+===========================================+
  48 | ``X``         | Any type          | A type to compute the ``sizeof`` for.     |
  49 +---------------+-------------------+-------------------------------------------+
  50
  51
  52 Expression semantics
  53 --------------------
  54
  55 For an arbitrary type ``x``:
  56
  57
  58 .. parsed-literal::
  59
  60     typedef sizeof_<x>::type n;
  61
  62
  63 :Return type:
  64     |Integral Constant|.
  65
  66 :Precondition:
  67     ``x`` is a complete type.
  68
  69 :Semantics:
  70     Equivalent to
  71
  72     .. parsed-literal::
  73
  74         typedef size_t< sizeof(x) > n;
  75
  76
  77
  78 Complexity
  79 ----------
  80
  81 Constant time.
  82
  83
  84 Example
  85 -------
  86
  87 .. parsed-literal::
  88
  89     struct udt { char a[100]; };
  90
  91     BOOST_MPL_ASSERT_RELATION( sizeof_<char>::value, ==, sizeof(char) );
  92     BOOST_MPL_ASSERT_RELATION( sizeof_<int>::value, ==, sizeof(int) );
  93     BOOST_MPL_ASSERT_RELATION( sizeof_<double>::value, ==, sizeof(double) );
  94     BOOST_MPL_ASSERT_RELATION( sizeof_<udt>::value, ==, sizeof(my) );
  95
  96
  97 See also
  98 --------
  99
 100 |Metafunctions|, |Integral Constant|, |size_t|
 101
 102
 103 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
 104    Distributed under the Boost Software License, Version 1.0. (See accompanying
 105    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)