is there nodiscard attribute available in c++11? If not, why no warning message output by g++ code belows. //test.cpp #include<iostream> [[nodiscard]] int foo() { return 1; } int main() { std::cout<<foo()<<std::endl; return 0; } At the beginning, i complie the program by "g++ -std=c++20 test.cpp -o test.o" and everythings is fine. But then i want… Read More No warning message generated by g++ when using [[nodiscard]] and compile with lower stl option

I’m reading the std::map part of The C++ Standard Library by Nicolai M. Josuttis. Here is a simplified code which can show the question bother me a lot: #include <iostream> #include <map> #include <string> class MyCompare { public: bool operator() (const std::string& lhs, const std::string& rhs) const { return lhs < rhs; } }; int… Read More why can I use a class as custom comparison criterion as a template argument to std::map without providing a class instance

Trying to sort an vector<pair<int,int>> decreasing order in C++. sort(v.begin(),v.end(),greater<int> ()) >Solution : The elements of your vector are pair<int,int>, so you should use greater<pair<int,int>> () instead of greater<int> ().

I’m learning std::set . Here is my codes: #include <set> #include <iostream> using namespace std; struct cmp{ bool operator () (const int & a,const int & b) const { if(abs(a-b)<=3) return false; return a < b; } }; set<int,cmp> q{1, 2, 10}; int main(){ if(q.find(4)!=q.end()) cout << 1; else cout << 2; } Output: 1… Read More c++ Overloaded operator () change std::set.find()

I want to create a dynamic memory for a car dealership for bikes and cars but the vector didn’t print the right things and has lots of repetitions that aren’t supposed to be there. I created an object for the overlapping variables for both vehicles so I can pass it through the bike class later… Read More Return the elements in an array using operator overloading with a class passing through it

While learning about how std::equal works, I was writing some test code and ran into this problem: #include <iostream> #include <vector> #include <algorithm> class Foo { public: std::vector<int> vec; Foo(std::vector<int> _vec) { vec = _vec; } std::vector<int> get() { return vec; } }; int main() { std::vector<int> x{ 1, 2, 3, 4, 5 }; std::vector<int>… Read More std::equal not working when using vectors returned by a getter

This is what my compare function looks like: bool smallest_weight(const size_t& i, const size_t& j) { return this->abs_weight[i] < this->abs_weight[j]; } I use this function inside the constructor of the class to initialize some other arrays. This is the code that uses it: size_t best_node = *min_element( this->pointer_list[i + 1].begin(), this->pointer_list[i + 1].end(), smallest_weight );… Read More How to use comparer function inside class with algorithm header?

I am currently declaring my vector as follows std::vector<std::vector<int>> test(5, std::vector<int>(2,0)); I then access it like this ` for (int i = 0; i < 5; i++) { std::cin >> test[i][0]; std::cin >> test[i][1]; } ` Since the vector is static (5 Rows, with 2 columns), I would like to make it variable (rows variable,… Read More Accessing a 2D vector using push_back()

I created a class MyString and overloaded operator==. MyString can be used without any problems class MyString { public: bool operator== (const MyString& obj) const; }; I want to use MyString as key in std::map. std::map<MyString, value> m_xxx; I can access the inserted data by iterating. for (auto& it : m_ini) { MyString first =… Read More std::map::find does not access operator==