forked from boostorg/core
92 lines
1.9 KiB
Plaintext
92 lines
1.9 KiB
Plaintext
[/
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Copyright 2019 Glen Joseph Fernandes
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(glenjofe@gmail.com)
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Distributed under the Boost Software License, Version 1.0.
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(http://www.boost.org/LICENSE_1_0.txt)
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]
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[section:first_scalar first_scalar]
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[simplesect Authors]
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* Glen Fernandes
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[endsimplesect]
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[section Overview]
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The header <boost/core/first_scalar.hpp> provides the function templates
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`boost::first_scalar` that can be used to obtain a pointer to the first scalar
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element of an array. Given a pointer of type `T*` they return a pointer of
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type `remove_all_extents_t<T>*`. The functions are `constexpr` and can be used
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in constant expressions.
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[endsect]
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[section Examples]
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The following function uses an allocator to allocate an array of arrays and
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constructs each scalar element in it.
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```
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#include <boost/alloc_construct.hpp>
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#include <boost/first_scalar.hpp>
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template<class A>
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auto create(const A& allocator)
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{
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typename std::allocator_traits<A>::template
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rebind_alloc<int[2][3]> other(allocator);
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auto ptr = other.allocate(4);
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try {
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boost::alloc_construct_n(other,
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boost::first_scalar(boost::to_address(ptr)), 24);
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} catch (...) {
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other.deallocate(ptr, 4);
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throw;
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}
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return ptr;
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}
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```
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[endsect]
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[section Reference]
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```
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namespace boost {
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template<class T>
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constexpr T* first_scalar(T* p) noexcept;
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template<class T, std::size_t N>
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constexpr auto first_scalar(T (*p)[N]) noexcept;
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} /* boost */
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```
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[section Functions]
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[variablelist
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[[`template<class T> constexpr T* first_scalar(T* p) noexcept;`]
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[[variablelist
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[[Returns][`p`.]]]]]
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[[`template<class T, std::size_t N> constexpr auto first_scalar(T (*p)[N])
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noexcept;`]
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[[variablelist
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[[Returns][`first_scalar(&(*p)[0])`.]]]]]]
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[endsect]
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[endsect]
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[section History]
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Glen Fernandes implemented `first_scalar`. Peter Dimov suggested a change for
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GCC to support an additional `constexpr` use.
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[endsect]
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[endsect]
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