Advertisements I’m trying to understand the difference in the following two cases. In both, I introduce a comparator as a lambda function: auto comp = [](int x, int y) { return x%2 < y%2; }; But then, if I want to use it with a sort, I can simply write sort(vec.begin(), vec.end(), comp); while for… Read More Using decltype for lambda comparators
Advertisements I have a Class called SceneManager with a method update that when the exit flag is true it switches the current scene to the using next = nextScene, but i don’t know why it doesn’t work, and the compiler isn’t helping much. I reproduced the problem in this compiler explorer space Link to Compiler… Read More Why cant i use alias type for constructing? C++
Advertisements I want to determine the type of this variable inside a class method. For example, take the following example – #include <iostream> #include <cstdlib> #include <map> class Base{ }; using getPrintString = std::map<Base, std::string>; class A : public Base{ public: void print(getPrintString& stringMap){ std::string toPrint = stringMap[std::remove_reference<decltype(*this)>::type]; std::cout<<toPrint<<std::endl; } }; class B: public Base{… Read More Getting type of Class inside a Class Method
Advertisements A minimized example of my code showing the problem: #include <cassert> #include <iostream> #include <map> #include <string> template <typename T> const std::map<std::string, T> smap; template <> const std::map<std::string, bool> smap<bool>{{"a", false}}; int main() { std::map<bool, std::string> rmap{{false, "x"}}; for (const auto& [key, val] : rmap) { std::cerr << typeid(bool).hash_code() << "\n"; std::cerr << typeid(decltype(key)).hash_code()… Read More Accessing variable template using decltype
Advertisements I’m new at programming and can someone explain to me how this code work? #include <iostream> using namespace std; int main () { int a = 3, b = 4; decltype(a) c = a; decltype((b)) d = a; ++c; ++d; cout << c << " " << d << endl; } I’m quite confused… Read More Why isn't the original value getting incremented twice even though I have two increments
Advertisements I have begun a project that makes heavy use of c++20 concepts as a way of learning some of the new c++20 features. As part of it, I have a function template that takes a single argument and operates on it. I wish to have the flexibility to pass types to this function that… Read More c++20 concepts: How can I use a type that may or may not exist?
Advertisements My question is why the following code is valid C++: #include <iostream> #include <tuple> #include <type_traits> std::tuple<const char *, const char *> tuple("Hello", "world"); std::integral_constant<std::size_t, 0> zero; std::integral_constant<std::size_t, 1> one; template<typename T> const char * lookup(T n) { // I would expect to have to write this: // return std::get<decltype(n)::value>(tuple); // But actually this… Read More Why does a non-constexpr std::integral_constant work as a template argument?
Advertisements I’d like a template function that returns some initialisation. I did the following: #include<iostream> #include<array> template <typename T> inline static constexpr T SetValues() { if(std::is_integral<T>::value) { std::cout<<"int\n"; return T{1}; } else { std::cout<<"array\n"; T arr = {1,2,3,4}; return arr; } } int main() { int a = 6; std::array<int, 4> arr = {2,2,2,2}; a… Read More How to initialise and return an std::array within a template function?
Advertisements I want to create some kind of Variant in C++. Actually I want to use templates as less as possible. The idea is to store the value in union both with the type of the variable and return the value according to the stored type. So the test code looks like following: #include <iostream>… Read More How to deduce a return type in C++