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<a href="a01019.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno"> 1</span> <span class="comment">// Aligned memory buffer -*- C++ -*-</span></div><div class="line"><a name="l00002"></a><span class="lineno"> 2</span> </div><div class="line"><a name="l00003"></a><span class="lineno"> 3</span> <span class="comment">// Copyright (C) 2013-2018 Free Software Foundation, Inc.</span></div><div class="line"><a name="l00004"></a><span class="lineno"> 4</span> <span class="comment">//</span></div><div class="line"><a name="l00005"></a><span class="lineno"> 5</span> <span class="comment">// This file is part of the GNU ISO C++ Library. This library is free</span></div><div class="line"><a name="l00006"></a><span class="lineno"> 6</span> <span class="comment">// software; you can redistribute it and/or modify it under the</span></div><div class="line"><a name="l00007"></a><span class="lineno"> 7</span> <span class="comment">// terms of the GNU General Public License as published by the</span></div><div class="line"><a name="l00008"></a><span class="lineno"> 8</span> <span class="comment">// Free Software Foundation; either version 3, or (at your option)</span></div><div class="line"><a name="l00009"></a><span class="lineno"> 9</span> <span class="comment">// any later version.</span></div><div class="line"><a name="l00010"></a><span class="lineno"> 10</span> </div><div class="line"><a name="l00011"></a><span class="lineno"> 11</span> <span class="comment">// This library is distributed in the hope that it will be useful,</span></div><div class="line"><a name="l00012"></a><span class="lineno"> 12</span> <span class="comment">// but WITHOUT ANY WARRANTY; without even the implied warranty of</span></div><div class="line"><a name="l00013"></a><span class="lineno"> 13</span> <span class="comment">// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the</span></div><div class="line"><a name="l00014"></a><span class="lineno"> 14</span> <span class="comment">// GNU General Public License for more details.</span></div><div class="line"><a name="l00015"></a><span class="lineno"> 15</span> </div><div class="line"><a name="l00016"></a><span class="lineno"> 16</span> <span class="comment">// Under Section 7 of GPL version 3, you are granted additional</span></div><div class="line"><a name="l00017"></a><span class="lineno"> 17</span> <span class="comment">// permissions described in the GCC Runtime Library Exception, version</span></div><div class="line"><a name="l00018"></a><span class="lineno"> 18</span> <span class="comment">// 3.1, as published by the Free Software Foundation.</span></div><div class="line"><a name="l00019"></a><span class="lineno"> 19</span> </div><div class="line"><a name="l00020"></a><span class="lineno"> 20</span> <span class="comment">// You should have received a copy of the GNU General Public License and</span></div><div class="line"><a name="l00021"></a><span class="lineno"> 21</span> <span class="comment">// a copy of the GCC Runtime Library Exception along with this program;</span></div><div class="line"><a name="l00022"></a><span class="lineno"> 22</span> <span class="comment">// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see</span></div><div class="line"><a name="l00023"></a><span class="lineno"> 23</span> <span class="comment">// <http://www.gnu.org/licenses/>.</span></div><div class="line"><a name="l00024"></a><span class="lineno"> 24</span> <span class="comment"></span></div><div class="line"><a name="l00025"></a><span class="lineno"> 25</span> <span class="comment">/** @file ext/aligned_buffer.h</span></div><div class="line"><a name="l00026"></a><span class="lineno"> 26</span> <span class="comment"> * This file is a GNU extension to the Standard C++ Library.</span></div><div class="line"><a name="l00027"></a><span class="lineno"> 27</span> <span class="comment"> */</span></div><div class="line"><a name="l00028"></a><span class="lineno"> 28</span> </div><div class="line"><a name="l00029"></a><span class="lineno"> 29</span> <span class="preprocessor">#ifndef _ALIGNED_BUFFER_H</span></div><div class="line"><a name="l00030"></a><span class="lineno"> 30</span> <span class="preprocessor">#define _ALIGNED_BUFFER_H 1</span></div><div class="line"><a name="l00031"></a><span class="lineno"> 31</span> </div><div class="line"><a name="l00032"></a><span class="lineno"> 32</span> <span class="preprocessor">#pragma GCC system_header</span></div><div class="line"><a name="l00033"></a><span class="lineno"> 33</span> </div><div class="line"><a name="l00034"></a><span class="lineno"> 34</span> <span class="preprocessor">#if __cplusplus >= 201103L</span></div><div class="line"><a name="l00035"></a><span class="lineno"> 35</span> <span class="preprocessor"># include <<a class="code" href="a00167.html">type_traits</a>></span></div><div class="line"><a name="l00036"></a><span class="lineno"> 36</span> <span class="preprocessor">#else</span></div><div class="line"><a name="l00037"></a><span class="lineno"> 37</span> <span class="preprocessor"># include <<a class="code" href="a00299.html">bits/c++0x_warning.h</a>></span></div><div class="line"><a name="l00038"></a><span class="lineno"> 38</span> <span class="preprocessor">#endif</span></div><div class="line"><a name="l00039"></a><span class="lineno"> 39</span> </div><div class="line"><a name="l00040"></a><span class="lineno"> 40</span> <span class="keyword">namespace </span><a class="code" href="a01547.html">__gnu_cxx</a></div><div class="line"><a name="l00041"></a><span class="lineno"> 41</span> {</div><div class="line"><a name="l00042"></a><span class="lineno"> 42</span>  <span class="comment">// A utility type containing a POD object that can hold an object of type</span></div><div class="line"><a name="l00043"></a><span class="lineno"> 43</span>  <span class="comment">// _Tp initialized via placement new or allocator_traits::construct.</span></div><div class="line"><a name="l00044"></a><span class="lineno"> 44</span>  <span class="comment">// Intended for use as a data member subobject, use __aligned_buffer for</span></div><div class="line"><a name="l00045"></a><span class="lineno"> 45</span>  <span class="comment">// complete objects.</span></div><div class="line"><a name="l00046"></a><span class="lineno"> 46</span>  <span class="keyword">template</span><<span class="keyword">typename</span> _Tp></div><div class="line"><a name="l00047"></a><span class="lineno"> 47</span>  <span class="keyword">struct </span>__aligned_membuf</div><div class="line"><a name="l00048"></a><span class="lineno"> 48</span>  {</div><div class="line"><a name="l00049"></a><span class="lineno"> 49</span>  <span class="comment">// Target macro ADJUST_FIELD_ALIGN can produce different alignment for</span></div><div class="line"><a name="l00050"></a><span class="lineno"> 50</span>  <span class="comment">// types when used as class members. __aligned_membuf is intended</span></div><div class="line"><a name="l00051"></a><span class="lineno"> 51</span>  <span class="comment">// for use as a class member, so align the buffer as for a class member.</span></div><div class="line"><a name="l00052"></a><span class="lineno"> 52</span>  <span class="comment">// Since GCC 8 we could just use alignof(_Tp) instead, but older</span></div><div class="line"><a name="l00053"></a><span class="lineno"> 53</span>  <span class="comment">// versions of non-GNU compilers might still need this trick.</span></div><div class="line"><a name="l00054"></a><span class="lineno"> 54</span>  <span class="keyword">struct </span>_Tp2 { _Tp _M_t; };</div><div class="line"><a name="l00055"></a><span class="lineno"> 55</span> </div><div class="line"><a name="l00056"></a><span class="lineno"> 56</span>  <span class="keyword">alignas</span>(__alignof__(_Tp2::_M_t)) <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> _M_storage[<span class="keyword">sizeof</span>(_Tp)];</div><div class="line"><a name="l00057"></a><span class="lineno"> 57</span> </div><div class="line"><a name="l00058"></a><span class="lineno"> 58</span>  __aligned_membuf() = <span class="keywordflow">default</span>;</div><div class="line"><a name="l00059"></a><span class="lineno"> 59</span> </div><div class="line"><a name="l00060"></a><span class="lineno"> 60</span>  <span class="comment">// Can be used to avoid value-initialization zeroing _M_storage.</span></div><div class="line"><a name="l00061"></a><span class="lineno"> 61</span>  __aligned_membuf(std::nullptr_t) { }</div><div class="line"><a name="l00062"></a><span class="lineno"> 62</span> </div><div class="line"><a name="l00063"></a><span class="lineno"> 63</span>  <span class="keywordtype">void</span>*</div><div class="line"><a name="l00064"></a><span class="lineno"> 64</span>  _M_addr() noexcept</div><div class="line"><a name="l00065"></a><span class="lineno"> 65</span>  { <span class="keywordflow">return</span> static_cast<void*>(&_M_storage); }</div><div class="line"><a name="l00066"></a><span class="lineno"> 66</span> </div><div class="line"><a name="l00067"></a><span class="lineno"> 67</span>  <span class="keyword">const</span> <span class="keywordtype">void</span>*</div><div class="line"><a name="l00068"></a><span class="lineno"> 68</span>  _M_addr() const noexcept</div><div class="line"><a name="l00069"></a><span class="lineno"> 69</span>  { <span class="keywordflow">return</span> static_cast<const void*>(&_M_storage); }</div><div class="line"><a name="l00070"></a><span class="lineno"> 70</span> </div><div class="line"><a name="l00071"></a><span class="lineno"> 71</span>  _Tp*</div><div class="line"><a name="l00072"></a><span class="lineno"> 72</span>  _M_ptr() noexcept</div><div class="line"><a name="l00073"></a><span class="lineno"> 73</span>  { <span class="keywordflow">return</span> static_cast<_Tp*>(_M_addr()); }</div><div class="line"><a name="l00074"></a><span class="lineno"> 74</span> </div><div class="line"><a name="l00075"></a><span class="lineno"> 75</span>  <span class="keyword">const</span> _Tp*</div><div class="line"><a name="l00076"></a><span class="lineno"> 76</span>  _M_ptr() const noexcept</div><div class="line"><a name="l00077"></a><span class="lineno"> 77</span>  { <span class="keywordflow">return</span> static_cast<const _Tp*>(_M_addr()); }</div><div class="line"><a name="l00078"></a><span class="lineno"> 78</span>  };</div><div class="line"><a name="l00079"></a><span class="lineno"> 79</span> </div><div class="line"><a name="l00080"></a><span class="lineno"> 80</span> <span class="preprocessor">#if _GLIBCXX_INLINE_VERSION</span></div><div class="line"><a name="l00081"></a><span class="lineno"> 81</span>  <span class="keyword">template</span><<span class="keyword">typename</span> _Tp></div><div class="line"><a name="l00082"></a><span class="lineno"> 82</span>  <span class="keyword">using</span> __aligned_buffer = __aligned_membuf<_Tp>;</div><div class="line"><a name="l00083"></a><span class="lineno"> 83</span> <span class="preprocessor">#else</span></div><div class="line"><a name="l00084"></a><span class="lineno"> 84</span>  <span class="comment">// Similar to __aligned_membuf but aligned for complete objects, not members.</span></div><div class="line"><a name="l00085"></a><span class="lineno"> 85</span>  <span class="comment">// This type is used in <forward_list>, <future>, <bits/shared_ptr_base.h></span></div><div class="line"><a name="l00086"></a><span class="lineno"> 86</span>  <span class="comment">// and <bits/hashtable_policy.h>, but ideally they would use __aligned_membuf</span></div><div class="line"><a name="l00087"></a><span class="lineno"> 87</span>  <span class="comment">// instead, as it has smaller size for some types on some targets.</span></div><div class="line"><a name="l00088"></a><span class="lineno"> 88</span>  <span class="comment">// This type is still used to avoid an ABI change.</span></div><div class="line"><a name="l00089"></a><span class="lineno"> 89</span>  <span class="keyword">template</span><<span class="keyword">typename</span> _Tp></div><div class="line"><a name="l00090"></a><span class="lineno"> 90</span>  <span class="keyword">struct </span>__aligned_buffer</div><div class="line"><a name="l00091"></a><span class="lineno"> 91</span>  : <a class="code" href="a04135.html">std::aligned_storage</a><sizeof(_Tp), __alignof__(_Tp)></div><div class="line"><a name="l00092"></a><span class="lineno"> 92</span>  {</div><div class="line"><a name="l00093"></a><span class="lineno"> 93</span>  <span class="keyword">typename</span></div><div class="line"><a name="l00094"></a><span class="lineno"> 94</span>  <a class="code" href="a04135.html">std::aligned_storage</a><<span class="keyword">sizeof</span>(_Tp), __alignof__(_Tp)>::type _M_storage;</div><div class="line"><a name="l00095"></a><span class="lineno"> 95</span> </div><div class="line"><a name="l00096"></a><span class="lineno"> 96</span>  __aligned_buffer() = <span class="keywordflow">default</span>;</div><div class="line"><a name="l00097"></a><span class="lineno"> 97</span> </div><div class="line"><a name="l00098"></a><span class="lineno"> 98</span>  <span class="comment">// Can be used to avoid value-initialization</span></div><div class="line"><a name="l00099"></a><span class="lineno"> 99</span>  __aligned_buffer(std::nullptr_t) { }</div><div class="line"><a name="l00100"></a><span class="lineno"> 100</span> </div><div class="line"><a name="l00101"></a><span class="lineno"> 101</span>  <span class="keywordtype">void</span>*</div><div class="line"><a name="l00102"></a><span class="lineno"> 102</span>  _M_addr() noexcept</div><div class="line"><a name="l00103"></a><span class="lineno"> 103</span>  {</div><div class="line"><a name="l00104"></a><span class="lineno"> 104</span>  <span class="keywordflow">return</span> static_cast<void*>(&_M_storage);</div><div class="line"><a name="l00105"></a><span class="lineno"> 105</span>  }</div><div class="line"><a name="l00106"></a><span class="lineno"> 106</span> </div><div class="line"><a name="l00107"></a><span class="lineno"> 107</span>  <span class="keyword">const</span> <span class="keywordtype">void</span>*</div><div class="line"><a name="l00108"></a><span class="lineno"> 108</span>  _M_addr() const noexcept</div><div class="line"><a name="l00109"></a><span class="lineno"> 109</span>  {</div><div class="line"><a name="l00110"></a><span class="lineno"> 110</span>  <span class="keywordflow">return</span> static_cast<const void*>(&_M_storage);</div><div class="line"><a name="l00111"></a><span class="lineno"> 111</span>  }</div><div class="line"><a name="l00112"></a><span class="lineno"> 112</span> </div><div class="line"><a name="l00113"></a><span class="lineno"> 113</span>  _Tp*</div><div class="line"><a name="l00114"></a><span class="lineno"> 114</span>  _M_ptr() noexcept</div><div class="line"><a name="l00115"></a><span class="lineno"> 115</span>  { <span class="keywordflow">return</span> static_cast<_Tp*>(_M_addr()); }</div><div class="line"><a name="l00116"></a><span class="lineno"> 116</span> </div><div class="line"><a name="l00117"></a><span class="lineno"> 117</span>  <span class="keyword">const</span> _Tp*</div><div class="line"><a name="l00118"></a><span class="lineno"> 118</span>  _M_ptr() const noexcept</div><div class="line"><a name="l00119"></a><span class="lineno"> 119</span>  { <span class="keywordflow">return</span> static_cast<const _Tp*>(_M_addr()); }</div><div class="line"><a name="l00120"></a><span class="lineno"> 120</span>  };</div><div class="line"><a name="l00121"></a><span class="lineno"> 121</span> <span class="preprocessor">#endif</span></div><div class="line"><a name="l00122"></a><span class="lineno"> 122</span> </div><div class="line"><a name="l00123"></a><span class="lineno"> 123</span> } <span class="comment">// namespace</span></div><div class="line"><a name="l00124"></a><span class="lineno"> 124</span> </div><div class="line"><a name="l00125"></a><span class="lineno"> 125</span> <span class="preprocessor">#endif </span><span class="comment">/* _ALIGNED_BUFFER_H */</span><span class="preprocessor"></span></div><div class="ttc" id="a00167_html"><div class="ttname"><a href="a00167.html">type_traits</a></div></div>
<div class="ttc" id="a04135_html"><div class="ttname"><a href="a04135.html">std::aligned_storage</a></div><div class="ttdoc">Alignment type.</div><div class="ttdef"><b>Definition:</b> <a href="a00167_source.html#l01800">type_traits:1800</a></div></div>
<div class="ttc" id="a01547_html"><div class="ttname"><a href="a01547.html">__gnu_cxx</a></div><div class="ttdoc">GNU extensions for public use.</div></div>
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