c++-standard-library

I was reviewing some older code of mine and I saw the code using pointers to implement a tree of Variant objects. It is a tree because each Variant can contain an unordered_map of Variant* . I looked at the code and wondered why isn't it just using values, a std::vector<Variant> , and std::unordered_map<std::string, Variant> , instead of Variant* . So I went ahead and changed it. It seemed okay except one thing, I got errors : /usr/local/include/c++/6.1.0/bits/stl_pair.h:153:11: error: 'std::pair<_T1, _T2>::second' has incomplete type _T2 second; /// @c second is a copy of the second object ^~

Is there a utility in the standard library to get the index of a given type in std::variant ? Or should I make one for myself? That is, I want to get the index of B in std::variant<A, B, C> and have that return 1 . There is std::variant_alternative for the opposite operation. Of course, there could be many same types on std::variant 's list, so this operation is not a bijection, but it isn't a problem for me (I can have first occurrence of type on list, or unique types on std::variant list). We could take advantage of the fact that index() almost already does the right thing. We can't

I need a "string pool" object into which I can repeatedly insert a "sequence of chars" (I use this phrase to mean "string" without confusing it with std::string or a C string), obtain a pointer to the sequence, and be guaranteed that the pointer will not become invalidated if/when the pool needs to grow. Using a simple std::string as the pool won't work, because of the possibility for the string to be reallocated when it outgrows its initial capacity, thus invalidating all previous pointers into it. The pool will not grow without bound -- there are well-defined points at which I will call a

What's the difference between input iterators and read-only forward iterators? Because the latter are read-only, they obviously don't satisfy requirements of output iterators. And, because of that, they're effectively input iterators with additional guarantees (if any). The problem is, what additional guarantees? My guess would be that forward iterators are multi-pass and input iterators are not, am I right? Yes, input iterators are one-pass iterators. You can only iterate over them once, while forward iterators are multi-pass. From §24.2.3 [input.iterators] p2 (the table) , pre-/postcondition

I get the error message "stoi is not a member of std" when I try to use std::stoi and try to compile it. I'm using g++ 4.7.2 from the command line so it can't be IDE error, I have all my includes in order, and g++4.7.2 defaults to using c++11. If it helps, my OS is Ubuntu 12.10. Is there something I haven't configured? #include <iostream> #include <string> using namespace std; int main(){ string theAnswer = "42"; int ans = std::stoi(theAnswer, 0, 10); cout << "The answer to everything is " << ans << endl; } Will not compile. But there's nothing wrong with it. std::stoi() is new in C++11 so you

I have a problem that sscanf solves (extracting things from a string). I don't like sscanf though since it's not type-safe and is old and horrible. I want to be clever and use some more modern parts of the C++ standard library. What should I use instead? Try std::stringstream : #include <sstream> ... std::stringstream s("123 456 789"); int a, b, c; s >> a >> b >> c; For most jobs standard streams do the job perfectly, std::string data = "AraK 22 4.0"; std::stringstream convertor(data); std::string name; int age; double gpa; convertor >> name >> age >> gpa; if(convertor.fail() == true) { // if