我在检查 Qt 源代码时遇到了以下代码:
template <typename T>
Q_INLINE_TEMPLATE void QList<T>::node_construct(Node *n, const T &t)
{
if (QTypeInfo<T>::isLarge || QTypeInfo<T>::isStatic) n->v = new T(t);
else if (QTypeInfo<T>::isComplex) new (n) T(t);
#if (defined(__GNUC__) || defined(__INTEL_COMPILER) || defined(__IBMCPP__)) && !defined(__OPTIMIZE__)
// This violates pointer aliasing rules, but it is known to be safe (and silent)
// in unoptimized GCC builds (-fno-strict-aliasing). The other compilers which
// set the same define are assumed to be safe.
else *reinterpret_cast<T*>(n) = t;
#else
// This is always safe, but penaltizes unoptimized builds a lot.
else ::memcpy(n, static_cast<const void *>(&t), sizeof(T));
#endif
}
它有一个奇怪的new
指令:
new (n) T(t);
据我了解,它似乎不是类型转换。这个结构是什么意思?