I'm trying to use QString as the key in a std::unordered_map, however I get the error: error C2280: 'std::hash<_Kty>::hash(const std::hash<_Kty> &)': attempting to reference a deleted ...

I have some random test parameters for which I need to calculate a hash to detect if I ran with same parameters. I might run the test using the same source recompiled at a different time or run on ...

#include <iostream> int main() { std::hash<int> hash_f; std::cout << hash_f(0) << std::endl; std::cout << hash_f(1) << std::endl; std::cout << hash_f(...

I thought it would have been, but I can't find this in my standard library implementation (gcc-4.8.2). Why is std::hash not already specialised for std::reference_wrapper? #pragma once #include &...

With a Regular Type, I mean the definition of Stepanov in Elements of Programming, basically, that there's the concept of equality and that objects which are copies of each other compare equal. So...

I was trying to specialize hash for my own type, a templated key. I was basing it off cppreference. I get the compile error "The C++ Standard doesn't provide a hash for this type". I figure I jus...

Can the C++11 std::hash type be used to hash function pointers? There is a hash partial specialization defined as template <typename T> struct hash<T*>; but since function pointers a...

Is the floating point specialisation of std::hash (say, for doubles or floats) reliable regarding almost-equality? That is, if two values (such as (1./std::sqrt(5.)/std::sqrt(5.)) and .2) should co...

I have defined this template class structure: template<typename T> struct Outer { struct Inner { /* ...some stuff... */ }; }; I want to put Inner objects into an unordered_map (actually, ...

I have a class (call it Outer) which has a private member class (Inner). I want to store instances of Outer::Inner in unordered standard containers, so I want to specialize std::hash<Outer::Inne...

I have an abstract base class Hashable that classes that can be hashed derive from. I would now like to extend std::hash to all classes that derive from Hashable. The following code is supposed to...

After reading the discussion on operator< for std::weak_ptr, I can't see any reason why defining std::hash to use the control block for std::weak_ptr wouldn't work. I also can't believe that thi...

Standard library implements std::hash as a template struct that is specialized for different types. It is used like this: #include <iostream> #include <functional> int main() { std::...

I can replace the actual implementation of std::hash with my own definition of std::hash in C++ 11 ? I mean from my codebase, without touching the standard library. I can't see any use for virtua...

Hi I have a question on std::hash if I have 2 large strings for comparison and I am willing to accept that std::hash will compare equal in most cases is it more performance compliant to do somethin...

I'm guessing std::hash is defined as a template struct in order to avoid implicit type conversions done during overloaded function resolution. Is it a correct thing to say? I mean, I would prefer t...

Why doesn't the C++ standard specify that std::hash<T> is specialized for char*, const char*, unsigned char*, const unsigned char*, etc? I.e., it would hash the contents of the C string until...

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...

If I did std::hash using libstdc++ and then did one on the upcoming C++11 VS 2012 library - would they match? I assume that hash implementations are not part of the C++ specification and can vary ...

I know hashing infinite number of string into 32b int must generate collision, but I expect from hashing function some nice distribution. Isn't it weird that these 2 strings have the same hash? s...