projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
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 |