cpp

[Martins3]

• [x] constexpr

[Martins3]

cpp primer

• [x] section 7.5
• [ ] https://hackingcpp.com/cpp/cheat_sheets.html
• [ ] union

[Martins3]

• [ ] c++20 's filesystem and concurrency programming

[Martins3]

objects

primer

• [x] 7.5
• [x] 15.7
• [x] 18.3
• [ ] 12.2
• [ ] 19.1

[Martins3]

1. create my comparator for a map

   auto comp = [](const string& a, const string& b) { return a.length() < b.length(); };
   map<string, string, decltype(comp)> my_map(comp);

   comp is used in two place!

But, for hash containers, it's a bottle more tricky: https://stackoverflow.com/questions/17016175/c-unordered-map-using-a-custom-class-type-as-the-key

2. priority_queue use similar style too !

   auto f = [](const MyStruct &struct1, const MyStruct &struct2) {
   return (struct1.key < struct2.key);
   };
   priority_queue<MyStruct, vector<MyStruct>, decltype(f)> b(f);

   sort : lambda, container : decltype

[Martins3]

If k does not match the key of any element in the container, the function inserts a new element with that key and returns a reference to its mapped value.

[Martins3]

• [x] how greater works?

  std::priority_queue<std::pair<int, int>, std::vector<std::pair<int, int>>,
                      std::greater<std::pair<int, int>>>

  FF should define < operator

  1. two const
  2. https://stackoverflow.com/questions/56905128/c-use-stdgreater-in-priority-queue-and-sort

     
     class FF {
     public:
     int x;
     int y;
     bool operator < (const FF &right) const { return this.x < FF.x; } 
     bool operator > (const FF &right) const { return this.x > FF.x; } 
     };
     typedef pair<int, FF> Elm;

  priority_queue<Elm, vector, std::greater> pq;