c++11

问题 Why decltype of constexpr variable is failed ? #include <cstdint> #include <type_traits> constexpr uint16_t foo(){ return 0;} constexpr auto cv = foo(); auto v = foo(); static_assert( std::is_same< uint16_t, decltype(cv)>::value, "!"); // failed static_assert( std::is_same< uint16_t, decltype(v) >::value, "!"); // success 回答1: decltype(entity) specifies the declared type of the entity specified by this expression. Due to the constexpr, ( A constexpr specifier used in an object declaration

问题 Why decltype of constexpr variable is failed ? #include <cstdint> #include <type_traits> constexpr uint16_t foo(){ return 0;} constexpr auto cv = foo(); auto v = foo(); static_assert( std::is_same< uint16_t, decltype(cv)>::value, "!"); // failed static_assert( std::is_same< uint16_t, decltype(v) >::value, "!"); // success 回答1: decltype(entity) specifies the declared type of the entity specified by this expression. Due to the constexpr, ( A constexpr specifier used in an object declaration

问题 I have the following code: #include <string> #include <vector> #include <iostream> class Test final { public: Test(const std::string& s) : s_(s) { std::cout << "constructing: " << s_ << std::endl; } #ifdef NO_MOVE private: Test(const Test& t) = delete; Test(Test&& t) = delete; #else public: Test(const Test& t) : s_(t.s_) { std::cout << "copying: " << s_ << std::endl; }; Test(Test&& t) : s_(std::move(t.s_)) { std::cout << "moving: " << s_ << std::endl; }; #endif private: std::string s_; }; int

问题 One of the ancient anti-pattern is people checking error status and then returning fairly useless messages like "operation failed" instead of "operation failed because ...". I want C++ file I/O operations to fail with exception and get the error message on why it failed. Specifically I want ofstream object to raise exception when file creation fails and get bit more useful message such as "permission denied" or "No file or path". This is trivial to do in languages such as C# or Java or Python

问题 I want to create an object of std::array<T, N> but the problem is I can only use functions that return a constexpr type or compiler will complain. The problem here is that I need to calculate the length of this array based on another array's size which could be something like this: template <typename T> struct DataLength { template <typename iter> size_t maxPossibleLength(iter begin, iter end) { size_t m_size = 0; while (begin != end) { m_size = m_size << 8 | std::numeric_limits<T>::max(); /*

问题 The following code will construct array of 10 Foo objects with default Foo constructor: Foo foo[10]; but i don't want do this, i have havy foo constructor and later i will regenarate all foo objects one by one and assign (copy) it to elements of foo array, so there is no sense to initialize array, i want just reserve space for it and set it elements later. Just like in the case of int foo[10] when elements of foo will not be initialized without ={}. How can i do this without using std

问题 This question already has answers here : initializer_list and move semantics (8 answers) Closed 6 years ago . I'm wondering why initializer_list doesn't work with unique_ptr: std::vector<std::unique_ptr<int>> vptr = {std::make_unique<int>(1), std::make_unique<int>(2)}; do not compile. However: std::vector<std::unique_ptr<int>> vptr(2); vptr[0] =std::make_unique<int>(1); vptr[1] =std::make_unique<int>(2); compile. and std::vector<int*>vint={new int{1},new int{2}}; or std::vector<std::shared

问题 This question already has answers here : initializer_list and move semantics (8 answers) Closed 6 years ago . I'm wondering why initializer_list doesn't work with unique_ptr: std::vector<std::unique_ptr<int>> vptr = {std::make_unique<int>(1), std::make_unique<int>(2)}; do not compile. However: std::vector<std::unique_ptr<int>> vptr(2); vptr[0] =std::make_unique<int>(1); vptr[1] =std::make_unique<int>(2); compile. and std::vector<int*>vint={new int{1},new int{2}}; or std::vector<std::shared

问题 I have a game where certain game objects spawn all at once and then despawn as they get destroyed/killed. The game objects are elements in an std::vector , and I'd like to minimize memory usage. I'm used to the swap trick, std::vector<gameObject>(gameObjectVector.begin(), gameObjectVector.end()).swap(gameObjectVector); but I noticed the inbuilt shrink_to_fit() from C++11. However, it has linear complexity while the swap trick is constant. Isn't the swap trick superior in every way? 回答1: The

问题 While developing an application, I had the following problem. I wanted to return an empty std::list<string> when a given function pointer was null, or the result of that function otherwise. This is a simplified version of my code: typedef std::list<std::string> (*ParamGenerator)(); std::list<std::string> foo() { /* ... */ ParamGenerator generator = ...; if(generator) return generator(); else return {}; } However, I usually like to use the ternary ( ?: ) operator in these cases, so I tried