unordered-set

This question already has an answer here: Using C++11 unordered_set in Visual C++ and clang 1 answer I am trying to define an unordered_set like this: unordered_set<Point> m_Points; When I compile it, I get the following error: The C++ Standard doesn't provide a hash for this type. Class Point : class Point{ private: int x, y; public: Point(int a_x, int a_y) : x(a_x), y(a_y) {} ~Point(){} int getX()const { return x; } int getY()const { return y; } bool operator == (const Point& rhs) const{ return x == rhs.x && y == rhs.y; } bool operator != (const Point& rhs) const{ return !(*this == rhs); } }

So the library I use has an enum (say it's named LibEnum ). I need to have an std::unordered_set of LibEnum , but I get compilation error that there is no specialized std::hash for it. I could easily write it and just return the number of value (first element is 0, second 1 etc), but where exactly I should put this specialization and how should it look like? I can't modify the library sources. enum LibEnum { A, B, C, D}; std::unordered_set <LibEnum> mySet; //need std::hash for LibEnum //how should it look like? You can just specialise std::hash for your type: namespace std { template <> struct

I've seen people mention that a random element can be grabbed from an unordered_set in O(1) time. I attempted to do so with this: std::unordered_set<TestObject*> test_set; //fill with data size_t index = rand() % test_set.size(); const TestObject* test = *(test_set.begin() + index); However, unordered_set iterators don't support + with an integer. begin can be given a size_t param, but it is the index of a bucket rather than an element. Randomly picking a bucket then randomly picking an element within it would result in a very unbalanced random distribution. What's the secret to proper O(1)

I'am trying to use std::unordered_set in cross-platform C++ application. It compiles and works like a charm in Visual C++ under Windows, but generates a fatal compilation error on clang under Mac OS X. I want to know why it happens and what is the right way to get this working. Example code: // // Clang build cmdline: // $ clang++ ./set.cpp -Wall -Werror -Wfatal-errors -std=c++11 -stdlib=libc++ -o set.out // #include <iostream> #include <unordered_set> struct Point { int x, y; Point(int x = 0, int y = 0) { this->x = x; this->y = y; } bool operator==(Point const& p) const { return this->x == p

I wanted to have something like unordered_set<vector<pair<int,int>>> us; but even without pair: #include <vector> #include <unordered_set> using namespace std; int main() { unordered_set<vector<int>> um; } it fails: In file included from /usr/include/c++/4.8/bits/hashtable.h:35:0, from /usr/include/c++/4.8/unordered_set:47, from prog.cpp:2: /usr/include/c++/4.8/bits/hashtable_policy.h: In instantiation of ‘struct std::__detail::_Hash_code_base<std::vector<int>, std::vector<int>, std::__detail::_Identity, std::hash<std::vector<int> >, std::__detail::_Mod_range_hashing, std::__detail::_Default

The following program does not compile an unordered set of pairs of integers, but it does for integers. Can unordered_set and its member functions be used on user-defined types, and how can I define it? #include <unordered_set> ... class A{ ... private: std::unordered_set< std::pair<int, int> > u_edge_; }; Compiler error: error: no matching function for call to 'std::unordered_set >::unordered_set()' Your code compiles on VS2010 SP1 (VC10), but it fails to compile with GCC g++ 4.7.2. However, you may want to consider boost::hash from Boost.Functional to hash a std::pair (with this addition,