custom comparator in set of struct

To create a custom comparator for a set of structs in C++, you can define a comparison function or overload the less-than operator (<). The comparator function should take two arguments of the struct type and return a boolean value indicating whether the first argument should be considered less than the second argument.

Here are the steps to create a custom comparator for a set of structs in C++:

  1. Define the struct: Define the struct with the desired fields that you want to compare. For example, let's say we have a struct called Person with two fields: name and age.

  2. Define the comparator function: Define a function that will be used as the custom comparator for the set. The function should take two arguments of the struct type and return a boolean value indicating the comparison result. For example, let's define a function called comparePersons:

cpp bool comparePersons(const Person& p1, const Person& p2) { // Comparison logic goes here }

  1. Implement the comparison logic: Inside the comparator function, implement the logic to compare the desired fields of the struct. For example, if you want to compare the name field, you can use the std::string's operator< to compare the names. If the name field is equal, you can then compare the age field. Return true if the first argument should be considered less than the second argument, and false otherwise. For example:

cpp bool comparePersons(const Person& p1, const Person& p2) { if (p1.name < p2.name) { return true; } else if (p1.name == p2.name) { return p1.age < p2.age; } else { return false; } }

  1. Create a set with the custom comparator: To create a set of structs using the custom comparator, specify the comparator function as the second template argument of the std::set container. For example:

cpp std::set<Person, decltype(comparePersons)*> personsSet(comparePersons);

The decltype(comparePersons)* specifies the type of the comparator function pointer.

  1. Use the set: You can now use the set as usual, and it will maintain the elements in the specified order according to the custom comparator. For example, you can insert elements into the set:

```cpp Person p1{"John", 30}; Person p2{"Alice", 25}; Person p3{"Bob", 35};

personsSet.insert(p1); personsSet.insert(p2); personsSet.insert(p3); ```

The set will automatically order the elements based on the custom comparator function.

Remember to include the necessary headers (<set> and <string>) and declare the struct and comparator function before using them.