Question

How to sort a vector of structs that contain nested structs using custom comparison logic in C++

Answer 1

#include <algorithm>   // for std::sort
#include <iostream>    // for std::cout
#include <string>      // for std::string
#include <vector>      // for std::vector
 
// ------------------------------------------------------------
// Example: Sorting a vector of structs that contain nested structs
// ------------------------------------------------------------
 
// A nested struct representing an address
struct Address {
    std::string city;
    int zip;
};
 
// A struct representing a person, containing a nested Address
struct Person {
    std::string name;
    int age;
    Address address;
};
 
// ------------------------------------------------------------
// Comparison function:
// Sort by city name first, then by zip code, then by age.
// This demonstrates how to naturally access nested fields.
// ------------------------------------------------------------
bool comparePersons(const Person& a, const Person& b) {
    // Compare by city
    if (a.address.city != b.address.city)
        return a.address.city < b.address.city;
 
    // If cities are equal, compare by zip
    if (a.address.zip != b.address.zip)
        return a.address.zip < b.address.zip;
 
    // If zip codes are equal, compare by age
    return a.age < b.age;
}
 
// ------------------------------------------------------------
// Helper function to print the list
// ------------------------------------------------------------
void printPersons(const std::vector<Person>& people) {
    for (const auto& p : people) {
        std::cout << p.name
                  << " | age: " << p.age
                  << " | city: " << p.address.city
                  << " | zip: " << p.address.zip
                  << "\n";
    }
}
 
// ------------------------------------------------------------
// Main program
// ------------------------------------------------------------
int main() {
    // Create a sample list of people
    std::vector<Person> people = {
        {"Alice", 30, {"San Francisco", 42100}},
        {"Bob",   40, {"Austin",   32000}},
        {"Carol", 35, {"New York City", 42000}},
        {"Dave",  25, {"Austin",   32000}},
        {"Eve",   28, {"New York City",61000}}
    };
 
    // Sort using std::sort and our custom comparison function
    std::sort(people.begin(), people.end(), comparePersons);
 
    // Print the sorted result
    printPersons(people);
}
 
 
 
/*
run:
 
Dave | age: 25 | city: Austin | zip: 32000
Bob | age: 40 | city: Austin | zip: 32000
Carol | age: 35 | city: New York City | zip: 42000
Eve | age: 28 | city: New York City | zip: 61000
Alice | age: 30 | city: San Francisco | zip: 42100
 
*/
 

 

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