c++11 – Page 28 – Tarik Billa

Using a std::unordered_set of std::unique_ptr

December 2, 2023 by Tarik

You can also use a deleter that optionally doesn’t do anything. template<class T> struct maybe_deleter{ bool _delete; explicit maybe_deleter(bool doit = true) : _delete(doit){} void operator()(T* p) const{ if(_delete) delete p; } }; template<class T> using set_unique_ptr = std::unique_ptr<T, maybe_deleter<T>>; template<class T> set_unique_ptr<T> make_find_ptr(T* raw){ return set_unique_ptr<T>(raw, maybe_deleter<T>(false)); } // … int* raw = new … Read more

Design principles behind std::ratio

December 2, 2023 by Tarik

When N2661 was proposed, none of the proposal authors had access to a compiler which implemented constexpr. And none of us were willing to propose something we could not build and test. So whether or not a better design could have been done with constexpr was not even part of the consideration for the design. … Read more

Define variable b of the same type as variable a

December 1, 2023 by Tarik

Sure, use decltype: auto var_a = bar(t); decltype(var_a) b; You can add cv-qualifiers and references to decltype specifiers as if it were any other type: const decltype(var_a)* b;

std::thread pass by reference calls copy constructor

December 1, 2023 by Tarik

std::thread takes its arguments by value. You can get reference semantics back by using std::reference_wrapper: std::thread newThread(session, &sock, std::ref(logger)); Obviously you must make sure that logger outlives the thread.

Custom allocator in std::vector

November 29, 2023 by Tarik

You basically have to implement your allocator type to conform to the Allocator concept. The linked page lists all requirements of that type, but the core functionality is implemented in the allocate member function.

What is the difference between using explicit fences and std::atomic?

November 29, 2023 by Tarik

Although various answers cover bits and pieces of what the potential problem is and/or provide useful information, no answer correctly describes the potential issues for all three cases. In order to synchronize memory operations between threads, release and acquire barriers are used to specify ordering. In the diagram, memory operations A in thread 1 cannot … Read more

unique_ptr lambda custom deleter for array specialization [duplicate]

November 29, 2023 by Tarik

What about: auto deleter=[&](int* ptr){…}; std::unique_ptr<int[], decltype(deleter)> ptr4(new int[4], deleter);

Set CPU affinity when create a thread

November 29, 2023 by Tarik

I am sorry to be the “myth buster” here, but setting thread affinity has great importance, and it grows in importance over time as the systems we all use become more and more NUMA (Non-Uniform Memory Architecture) by nature. Even a trivial dual socket server these days has RAM connected separately to each socket, and … Read more

Implementation of addressof

November 28, 2023 by Tarik

First you have __r which is of type _Tp& It is reinterpret_cast‘ed to a char& in order to ensure being able to later take its address without fearing an overloaded operator& in the original type; actually it is cast to const volatile char& because reinterpret_cast can always legally add const and volatile qualifiers even if … Read more

Why is “error: invalid application of ‘sizeof’ to an incomplete type using unique_ptr” fixed by adding an empty destructor? [duplicate]

November 28, 2023 by Tarik

If we go to the cppreference document for std::unique_ptr: std::unique_ptr may be constructed for an incomplete type T, such as to facilitate the use as a handle in the Pimpl idiom. If the default deleter is used, T must be complete at the point in code where the deleter is invoked, which happens in the … Read more