initializer-list

问题 In C++11, one can use initializer lists to initialize parameters in functions. What is the purpose of it? Can't the same be done with const vectors? What is the difference of the two programs below? Using an initializer list: #include <iostream> using namespace std; int sumL(initializer_list<int> l){ int sum = 0; for (const auto i: l){ sum += i; } return sum; } int main(){ cout << sumL({1, 2, 3}) << "\n"; return 0; } Using a const vector: #include <iostream> #include <vector> using namespace

问题 I am implementing a container in c++, a wrapper for an array in fact. I am not sure how to implement a constructor from initializer_list. I end up with this implementation but it seems to me really ugly. So could be an array allocated in a heap initialized by an initializer_list. Or is there an elegant way how to do it? template <typename T> class sequence { public: sequence (size_t n): _data {new T[n]}, _size {n} {}; sequence (std::initializer_list<T> source); ~sequence() { delete[] _data; }

问题 I'm trying to initialize a big array of elements with the same initializer. 64 elements is just an example — I want to make it at least 16k. Unfortunately a simple let array : [AllocatedMemory<u8>; 64] = [AllocatedMemory::<u8>{mem:&mut []};64]; won't work because the AllocatedMemory struct does not implement Copy error: the trait `core::marker::Copy` is not implemented for the type `AllocatedMemory<'_, u8>` [E0277] let array : [AllocatedMemory<u8>; 64] = [AllocatedMemory::<u8>{mem:&mut []};

问题 Consider the code below: #include <iostream> #include <vector> void f(std::vector<int> v) {std::cout << __PRETTY_FUNCTION__ << std::endl;} void f(int n) {std::cout << __PRETTY_FUNCTION__ << std::endl;} int main() { f({42}); // the int overload is being picked up } Live on Coliru I was a bit surprised to realize that in this case the int overload is being picked up, i.e. the output of the program is: void f(int) with the warning warning: braces around scalar initializer [-Wbraced-scalar-init]

问题 So I have a lambda who's return type is auto and I'm having issues with the array backing for an initializer_list being destroyed here: const auto foo = [](const auto& a, const auto& b, const auto& c) { return {a, b, c}; }; I will be using the lambda like this: auto bar = foo(1, 2, 3); for(const auto& i : bar) cout << i << endl; A job that I'm working has as part of their coding standard that all lambdas are single statements (feel free to express your outrage.) I think that I can get around

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Can I list-initialize a vector of move-only type? Edit 1: Please consider a re-open vote: My question emphasize in-place construction. Move construction is an alternative but not what this questions is about. Thanks for the answers! Edit 2: Since I can't answer this question (It got closed) I post my own suggestion here. The following is not as good as the answers I accepted, but may be useful for others. At

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Can I list-initialize a vector of move-only type? Edit 1: Please consider a re-open vote: My question emphasize in-place construction. Move construction is an alternative but not what this questions is about. Thanks for the answers! Edit 2: Since I can't answer this question (It got closed) I post my own suggestion here. The following is not as good as the answers I accepted, but may be useful for others. At

问题 This is a follow-up to an earlier question about why I can't use a brace-enclosed initializer as an argument to operator+, which was resolved by looking at this earlier question on the subject. Consider the following C++ code, which you can try live at ideone.com: #include <iostream> #include <initializer_list> using namespace std; struct AddInitializerList { void operator+= (initializer_list<int> values) { // Do nothing } void operator+ (initializer_list<int> values) { // Do nothing } }; int

问题 Initializing objects with new {} syntax like this: int a { 123 }; has benefit - you would not declare a function instead of creating a variable by mistake. I even heard that it should be habit to always do that. But see what could happen: // I want to create vector with 5 ones in it: std::vector<int> vi{ 5, 1 }; // ups we have vector with 5 and 1. Is this good habit then? Is there a way to avoid such problems? 回答1: Frankly, the subtleties of the various initialization techniques make it

问题 I don't understand the error message when trying to pass a variable number of initializer lists: template<typename... Values> void foo(Values...) { } int main() { foo(1, 2, 3, "hello", 'a'); // OK foo({1}, {2, 3}); // ERROR } The error message complains about too many arguments: prog.cpp: In function ‘int main()’: prog.cpp:9:20: error: too many arguments to function ‘void foo(Values ...) [with Values = {}]’ foo({1}, {2, 3}); ^ prog.cpp:2:6: note: declared here void foo(Values...) ^ However,