My reading of the standard is that std::memcpy is safe whenever the type is trivially copyable. From 9 Classes, we can see that unions are class types and so trivially copyable applies to them. A union is a class defined with the class-key union; it holds only one data member at a time (9.5). A … Read more
Word “thread” could mean several things here: System.Threading.Thread object (created by new Thread()), CLR thread (managed thread), OS thread (un-managed thread). Thread object will be candidate for GC as soon as Start() method completes, because there are no more references to it. Managed thread will stay alive while doSomeLengthyOperation() runs. Quoting the article by James … Read more
This is a bug in gcc 4.8 that has been fixed in 4.9. Here is the bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50025
If the lifetime ends before the destructor starts, doesn’t that mean accessing members in the destructor is undefined behavior? Hopefully not: From N3242 Construction and destruction [class.cdtor] /3 To form a pointer to (or access the value of) a direct non-static member of an object obj, the construction of obj shall have started and its … Read more
getString() would return a copy of str (getString() returns by value); It’s right. thus, the copy of str would stay “alive” in main() until main() returns. No, the returned copy is a temporary std::string, which will be destroyed at the end of the statement in which it was created, i.e. before std::cout << cStr << … Read more
§5.1.2/6 says: The closure type for a lambda-expression with no lambda-capture has a public non-virtual non-explicit const conversion function to pointer to function having the same parameter and return types as the closure type’s function call operator. The value returned by this conversion function shall be the address of a function that, when invoked, has … Read more
It is legal now, and retroactively since C++98! Indeed the C++ specification wording till C++20 was defining an object as (e.g. C++17 wording, [intro.object]): The constructs in a C++ program create, destroy, refer to, access, and manipulate objects. An object is created by a definition (6.1), by a new-expression (8.5.2.4), when implicitly changing the active … Read more
The Per Thread Lifetime is a very dangerous lifestyle and in general you should not use it in your application, especially web applications. This lifestyle should be considered dangerous, because it is very hard to predict what the actual lifespan of a thread is. When you create and start a thread using new Thread().Start(), you’ll … Read more
There are many articles that explain why you should never call virtual functions in constructor and destructor in C++. Take a look here and here for details what happens behind the scene during such calls. In short, objects are constructed from the base up to the derived. So when you try to call a virtual … Read more
Why would the behavior of std::memcpy itself be undefined when used with non-TriviallyCopyable objects? It’s not! However, once you copy the underlying bytes of one object of a non-trivially copyable type into another object of that type, the target object is not alive. We destroyed it by reusing its storage, and haven’t revitalized it by … Read more