41 lines
858 B
C++
41 lines
858 B
C++
/*
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* Copyright (C) 2014 Cloudius Systems, Ltd.
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*/
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#ifndef VLA_HH_
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#define VLA_HH_
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#include <memory>
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#include <new>
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#include <assert.h>
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#include <type_traits>
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// Some C APIs have a structure with a variable length array at the end.
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// This is a helper function to help allocate it.
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//
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// for a structure
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//
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// struct xx { int a; float b[0]; };
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//
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// use
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//
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// make_struct_with_vla(&xx::b, number_of_bs);
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//
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// to allocate it.
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//
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template <class S, typename E>
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inline
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std::unique_ptr<S>
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make_struct_with_vla(E S::*last, size_t nr) {
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auto fake = reinterpret_cast<S*>(0);
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size_t offset = reinterpret_cast<uintptr_t>(&(fake->*last));
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size_t element_size = sizeof((fake->*last)[0]);
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assert(offset == sizeof(S));
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auto p = ::operator new(offset + element_size * nr);
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return std::unique_ptr<S>(new (p) S());
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}
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#endif /* VLA_HH_ */
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