On 05/03/14 11:25 PM, comex wrote: > On Wed, Mar 5, 2014 at 6:22 AM, Michael Neumann <mneum...@ntecs.de> wrote: >> Try the same in C++: >> >> >> auto i = make_unique<int>(1234); >> auto j = std::move(i); >> cout << *j << endl; // 1234 >> cout << *i << endl; // Segmentation Fault > > Note that a move out of unique_ptr is guaranteed to leave the original > null, so while this is not detected at compile time, it's also not > memory-unsafe.
A null pointer dereference doesn't usually cause a segmentation fault in kernel code. It causes one in userspace because the first page is usually protected. However, the C and C++ standards consider a null pointer dereference to be undefined behaviour and GCC/LLVM encode this in their optimization engines. It's in no way safe to dereference a null pointer with LLVM as the compiler. Type-checked moved semantics and type-checked reference lifetimes are in my opinion the major safety improvements over C++. The other aspects of a smart pointer type *can* be equally safe in both languages, but the C++11 library smart pointers are not due to being nullable.
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