initializer-list

问题 In my code base I often initialize array or vector if bytes using the following the syntax: uint16_t foo = 0xAB, bar = 0xCD // bytes = { 0xA, 0xB, 0xC, 0xD } std::array<uint8_t, 4> bytes = {{ foo >> 8, foo & 0x00FF, bar >> 8, bar & 0x00FF }}; I get the following error from clang++: error: non-constant-expression cannot be narrowed from type 'int' to 'value_type' (aka 'unsigned char') in initializer list [-Wc++11-narrowing] foo >> 8, ^~~~~~~~~~~~~ The compiler suggest me to add a static_cast

问题 Consider the following code snippet from pg. 17 's A Tour of C++ : class Vector { public: Vector(int s) :elem{new double[s]}, sz{s} { } //construct a Vector double& operator[](int i) { return elem[i]; } //element access: subscripting int size() { return sz; } private: double* elem; // pointer to the elements int sz; // the number of elements }; Here I'm concerned about the member initializer list on the third line, where Stroustrup separates a colon from the two initializer statements elem

问题 I have a class that takes a "list" of pins as argument in the constructor. Right now, this "list" is just a const array ( const unsigned int (&pins)[N] ). I'd like to overload the constructor in such a way that you can use an initializer_list as well as a (const) array. I can get it working with separate classes, but I'm unable to combine them. The basic structure of my test class: #include <iostream> #include <cstring> using namespace std; class X { public: X(... pins); ~X(); void print() {

问题 Consider below program, #include <iostream> using namespace std; class A { public: A() { cout << "A constructor\n"; } void f() { cout << "A used\n"; this->i++; } private: int i; }; class B { public: B(A & a1) { cout << "B constructor\n"; a1.f(); } }; class Z { public: Z() : a_(), b_(a_) {} private: B b_; A a_; }; int main() { Z z; return 0; } Below is output it produces, B constructor A used A constructor My Question, Since data member objects are created in order of their declaration in

问题 Consider below program, #include <iostream> using namespace std; class A { public: A() { cout << "A constructor\n"; } void f() { cout << "A used\n"; this->i++; } private: int i; }; class B { public: B(A & a1) { cout << "B constructor\n"; a1.f(); } }; class Z { public: Z() : a_(), b_(a_) {} private: B b_; A a_; }; int main() { Z z; return 0; } Below is output it produces, B constructor A used A constructor My Question, Since data member objects are created in order of their declaration in

问题 Lets assume that I have a class with the following constructor: class Foo { Foo(std::initializer_list<uin8_t> args) { .... } } and I have the following array: std::array<uint8_t, 6> bar . Now I would like to create an object off foo with the bar array. Is there an other way as doing it in the follwing way: Foo f (bar[0], bar[1], bar[2], bar[3], bar[4], bar[5]); This way seems a bit complicated and it feels like this is not the way it should be. So, can I create a std::initializer list from an

问题 I'm currently tasked with creating a definition for a special custom class my professor provided to us; I've never seen initializer_list in use, nor did my professor go over it. What exactly does it do? template<class T> LinkedQueue<T>::LinkedQueue(const std::initializer_list<T>& il) { } I have to define the constructor, which I will do on my own. I just want to know what this parameter does. Also, my compiler keeps telling me that std::initializer_list member declaration is not found. I've

问题 I'm currently tasked with creating a definition for a special custom class my professor provided to us; I've never seen initializer_list in use, nor did my professor go over it. What exactly does it do? template<class T> LinkedQueue<T>::LinkedQueue(const std::initializer_list<T>& il) { } I have to define the constructor, which I will do on my own. I just want to know what this parameter does. Also, my compiler keeps telling me that std::initializer_list member declaration is not found. I've

问题 In the C++ code below, what is type of a ? typeid returns St16initializer_listIPKcE auto a = { "lol", "life" }; 回答1: When you have auto a = { "lol", "life" }; The compiler will try to deduce a std::initializer_list where the type is what all of the elements are. In this case "lol" and "life" are both a const char[] so you have a std::initializer_list<const char*> . If on the other have you had something like auto foo = { 1, 2.0 }; Then you would have a compiler error since the element types

问题 At the end of this video (starting at 15:57) there is advice on how to use almost uniform initialization in C++17: video here The gist goes like this: use always direct initialization auto a{...}; and MyType a{...}; Do not use copy initialization = {...} for your types. #include <iostream> struct MyType { explicit MyType(std::initializer_list<int>) { std::cout << "Called std::initializer_list<int>" << std::endl; } explicit MyType(int) { std::cout << "Called int." << std::endl; } MyType(int,