c++-standard-library

问题 I came across this question recently. My goal is to understand how the C++ compiler views struct definitions which hold standard library containers such as std::vector. Ben Voigt's answer to the linked question cites the following from the C++0x standard: .... A trivial class is a class that has a trivial default constructor (12.1) and is trivially copyable. [ Note: In particular, a trivially copyable or trivial class does not have virtual functions or virtual base classes. — end note ] A

问题 The pop() method of std::priority_queue is not declared noexcept , so in theory could throw an exception. But when might it throw an exception, and what might those exceptions be? 回答1: It could be marked nothrow , but isn't. Why std::priority_queue::pop could * not throw void pop(); Removes the top element from the priority queue. Effectively calls std::pop_heap(c.begin(), c.end(), comp); c.pop_back(); c is by default an std::vector . [vector.modifiers]/4&5 void pop_back(); 4/ Complexity :

问题 On my system, running Windows 7 x64, Eclipse Luna, and g++ 4.9.2 (installed via cygwin), it seems std::stoi was never declared by g++. According to the documentation, stoi is part of the string library, so obviously I have #include <string> . In addition, I know that stoi was introduced in C++11, and I have set the appropriate flags for my compiler (g++), even though this seems like an IDE error , rather than a compiler error. Still, I would get one of the following error messages when

问题 On my system, running Windows 7 x64, Eclipse Luna, and g++ 4.9.2 (installed via cygwin), it seems std::stoi was never declared by g++. According to the documentation, stoi is part of the string library, so obviously I have #include <string> . In addition, I know that stoi was introduced in C++11, and I have set the appropriate flags for my compiler (g++), even though this seems like an IDE error , rather than a compiler error. Still, I would get one of the following error messages when

问题 The bidirectional iterators have no luxuries like random access iterators, and hence need to depend upon the std::next and std::prev, when someone needs to do operations like std::set<int> s{ 1, 2, 3, 4, 5 }; //std::set<int> s2(s.cbegin(), s.cbegin() + 2); // won't work as there is no operator+ for std::set::const_iterator std::set<int> s2(s.cbegin(), std::next(s.cbegin(), 2)); //std::set<int> s3(s.cbegin(), s.cend() - 2); // won't work as there is no operator- for std::set::const_iterator

问题 The bidirectional iterators have no luxuries like random access iterators, and hence need to depend upon the std::next and std::prev, when someone needs to do operations like std::set<int> s{ 1, 2, 3, 4, 5 }; //std::set<int> s2(s.cbegin(), s.cbegin() + 2); // won't work as there is no operator+ for std::set::const_iterator std::set<int> s2(s.cbegin(), std::next(s.cbegin(), 2)); //std::set<int> s3(s.cbegin(), s.cend() - 2); // won't work as there is no operator- for std::set::const_iterator

问题 In most places where the C++ standard library allocates memory, the user is able to customise this by providing a class which meets the Allocator requirements. For example, almost all containers take an allocator template argument, and std::allocate_shared returns a shared_ptr whose contained element and control block are both allocated via a provided Allocator. However, there are a few places where the standard library can (potentially) allocate memory, but no Allocator support is provided.

问题 I'm unsure if it's me not understanding or the documentation isn't clearly formulated. The following excerpt has been taken from the newest draft (N3126, section 29.6): bool atomic_compare_exchange_weak(volatile A* object, C * expected, C desired); bool atomic_compare_exchange_weak(A* object, C * expected, C desired); bool atomic_compare_exchange_strong(volatile A* object, C * expected, C desired); bool atomic_compare_exchange_strong(A* object, C * expected, C desired); bool atomic_compare

问题 I'm unsure if it's me not understanding or the documentation isn't clearly formulated. The following excerpt has been taken from the newest draft (N3126, section 29.6): bool atomic_compare_exchange_weak(volatile A* object, C * expected, C desired); bool atomic_compare_exchange_weak(A* object, C * expected, C desired); bool atomic_compare_exchange_strong(volatile A* object, C * expected, C desired); bool atomic_compare_exchange_strong(A* object, C * expected, C desired); bool atomic_compare

问题 I'm unsure if it's me not understanding or the documentation isn't clearly formulated. The following excerpt has been taken from the newest draft (N3126, section 29.6): bool atomic_compare_exchange_weak(volatile A* object, C * expected, C desired); bool atomic_compare_exchange_weak(A* object, C * expected, C desired); bool atomic_compare_exchange_strong(volatile A* object, C * expected, C desired); bool atomic_compare_exchange_strong(A* object, C * expected, C desired); bool atomic_compare