It does not work because in {a,b} you are making a copy of a and b. One possible solution would be to make the loop variable a pointer, taking the addresses of a and b: #include <initializer_list> struct Obj { int i; }; Obj a, b; int main() { for(auto obj : {&a, &b}) { … Read more
Conceptually copy-list-initialization is the conversion of a compound value to a destination type. The paper that proposed wording and explained rationale already considered the term “copy” in “copy list initialization” unfortunate, since it doesn’t really convey the actual rationale behind it. But it is kept for compatibility with existing wording. A {10, 20} pair/tuple value … Read more
Use the appropriate constructor, which takes a size and a default value. int number_of_elements = 10; int default_value = 1; std::vector<int> vec(number_of_elements, default_value);
Your first line printme({‘a’, ‘b’, ‘c’}) is illegal because the template argument T could not be inferred. If you explicitly specify the template argument it will work, e.g. printme<vector<char>>({‘a’, ‘b’, ‘c’}) or printme<initializer_list<char>>({‘a’, ‘b’, ‘c’}). The other ones you listed are legal because the argument has a well-defined type, so the template argument T can … Read more
Indeed the final version of C++11 does not enable the use of initializer lists on the right-hand side (or left-hand side, for that matter) of a binary operator. Firstly, initializer-lists are not expressions as defined in ยง5 of the Standard. The arguments of functions, as well as of binary operators, generally have to be expressions, … Read more
According to Bjarne Stroustrup in Section 17.3.4.2 (p. 497) of The C++ Programming Language, 4th Edition: Unfortunately, initializer_list doesn’t provide subscripting. No further reason is given. My guess is that it’s one of these reasons: it’s an omission, or because the initializer_list class is implemented with an array and you’d have to do bounds checking … Read more
In general, is there a way to do this without wasted function calls or memory? Yes. This can be done with a delegating constructor, introduced in C++11. A delegating constructor is a very efficient way to acquire temporary values needed for construction before any member variables are initialized. int gcd(int a, int b); // Greatest … Read more
It can only be done for aggregates (arrays and certain classes. Contrary to popular belief, this works for many nonpods too). Writing a constructor that takes them is not possible. Since you tagged it as “C++0x”, then this is possible though. The magic words is “initializer-list constructor”. This goes like Phenotype(std::initializer_list<uint8> c) { assert(c.size() <= … Read more
What is happening here is that in the two element initializer list both of the string literals can be implicitly converted to const char* since their type is const char[N]. Now std::vector has a constructor that takes two iterators which the pointers qualify for. Because of that the initializer_list constructor of the std::vector<std::string> is conflicting … Read more
To make long story short: a braced initializer expression {} has no type by itself auto has to infer type information int{3} obviously means “create an int var with value taken from initializer list”, thus its type is just int and can be used in any wider context (int i = int{3} will work and … Read more