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[C++] Fix Undefined behavior for zero length vectors #5355

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Merged
aardappel merged 2 commits into from
May 30, 2019
Merged

[C++] Fix Undefined behavior for zero length vectors #5355

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d094b03
Fix Undefined behavior for zero length vectors
emkornfield May 20, 2019
acacd4d
Change fix for UBSan
emkornfield May 24, 2019
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10 changes: 8 additions & 2 deletions include/flatbuffers/flatbuffers.h
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Original file line number Diff line number Diff line change
Expand Up @@ -892,10 +892,16 @@ inline voffset_t FieldIndexToOffset(voffset_t field_id) {

template<typename T, typename Alloc>
const T *data(const std::vector<T, Alloc> &v) {
return v.empty() ? nullptr : &v.front();
// Eventually the returned pointer gets passed down to memcpy, so
// we need it to be non-null to avoid undefined behavior.
static uint8_t t;
return v.empty() ? reinterpret_cast<const T*>(&t) : &v.front();
}
template<typename T, typename Alloc> T *data(std::vector<T, Alloc> &v) {
return v.empty() ? nullptr : &v.front();
// Eventually the returned pointer gets passed down to memcpy, so
// we need it to be non-null to avoid undefined behavior.
static uint8_t t;
return v.empty() ? reinterpret_cast<T*>(&t) : &v.front();
}

/// @endcond
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