std

问题 I was reading through the std::thread documentation at cppreference (not always 100% accurate, I know) and noticed the following definition for the behavior of std::thread when passed a "pointer-to-data-member" (not "pointer-to-member-function") as its first argument ( f ) and an object of the required class as its second argument ( t1 after copying to thread-local-storage): If N == 1 and f is pointer to a member data object of a class, then it is accessed. The value of the object is ignored.

问题 What is the status of C++ TR2 Filesystem library as of last Bristol meeting? Will it be part of C++1Y (C++14?) or is it suspended or are there any known recent comments as of the last three meetings? 回答1: It has recently been unanimously approved by the ISO committee but did not make it in time for C++14. Though all the TSs (filesytem, library fundamentals, networking, etc.) are expected to be independently available ahead of C++17, I believe the intention is that if they are ready in time,

问题 I've got this class AppController and the function connectPlayer : /* AppController.h */ class AppController { // Some other declarations ... private: static const string TAG; }; /* AppController.cpp */ #include "AppController.h" const string AppController::TAG = "AppController"; AppController::AppController() { /* some code here...*/ } void AppController::connectPlayer() { std::string port; std::string host; port = CM->getMenu()->getData("PORT"); host = CM->getMenu()->getData("HOST"); this-

问题 I want to store data by both, their name and their index. In other words, I want to map string names to objects and also give them a custom order. What I came up with first is a std::vector of pairs of the string key and the object. The order was given by the position in the vector. std::vector<std::pair<std::string, object> > But this approach seems to be suboptimal since it doesn't automatically check for the uniqueness of string names. Moreover it feels wrong to group the objects by their

问题 I create two standard vector of unique_ptr: std::vector<std::unique_ptr<Student>> students; std::vector<std::unique_ptr<Teacher>> teachers; Then, I create a new object and put it in the vector: students.push_back(std::unique_ptr<Student> (new Student())); teachers.push_back(std::unique_ptr<Teacher> (new Teacher())); After all the operation I have to do, how can I delete the vector? Whitout unique_ptr I had to do a loop and delete each object: while (!students.empty()) { delete students.back()

问题 I recently heard new c++ standard features which are: std::latch std::barrier I cannot figure it out ,in which situations that they are applicable and useful over one-another. If someone can raise an example for how to use each one of them wisely it would be really helpful. 来源： https://stackoverflow.com/questions/48985967/where-can-we-use-stdbarrier-over-stdlatch

问题 In his keynote of this years Going Native The Essence of C++ (go to 40:30) Bjarne Stroustrup gives the following code example: template<typename C, typename V> vector<Value_type<C>*> find_all(C& cont, V v) { vector<Value_type<C>*> res; for (auto& x : cont) if (x == v) res.push_back(&x) return res; } This function is used to find all occurrences of a value in a container and returns pointers to the found elements. The example from the video: string m{"Mary had a little lamb"}; for (const auto

问题 With template functions from <algorithm> you can do things like this struct foo { int bar, baz; }; struct bar_less { // compare foo with foo bool operator()(const foo& lh, const foo& rh) const { return lh.bar < rh.bar; } template<typename T> // compare some T with foo bool operator()(T lh, const foo& rh) const { return lh < rh.bar; } template<typename T> // compare foo with some T bool operator()(const foo& lh, T rh) const { return lh.bar < rh; } }; int main() { foo foos[] = { {1, 2}, {2, 3},

问题 I am using std::copy to copy the objects in std::deque to a file. The code is working fine but I need to check if copying was successful and accordingly I need to set the flag or else throw exception. I have googled but could not find the solution how to check if std::copy has successfully copied the values into the file. Could someone please throw a light on it. 回答1: If writing to the file fails, then the file stream's error flags will be set - you can either check these after the copy, or

问题 Imagine such code: string f() { string r = "ab"; return r; } int main() { const char *c = f().c_str(); printf("%s.\n", c); return 0; } This code may crash, right? Because that string that c points to is destroyed. But running it via Valgrind doesn't show any invalid memory accesses. Why? I know Valgrind cannot check the stack, but "ab" actually is located on the heap, right? 回答1: This code may crash, right? Because that string that c points to is destroyed. Right. It has undefined behaviour,