Sorting

We can sort a vector using std::ranges::sort. This requires that we provide a function that tells sort how to compare 2 elements.

Here’s an example that sorts some strings using the default comparison (alphabetically) and then again with a custom comparison function that sorts by string length:

Listing 91 algorithms_functions.cpp

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

bool size_compare(const std::string& a, const std::string& b) {
    return a.size() < b.size();
}

int main() {

    std::vector<std::string> titles{"a new hope",
                                    "the empire strikes back",
                                    "return of the jedi",
                                    "the phantom menace",
                                    "attack of the clones",
                                    "revenge of the sith",
                                    "the force awakens",
                                    "the last jedi",
                                    "the rise of skywalker"};

    std::ranges::sort(titles);

    for (const auto& e : titles) {
        std::cout << e << std::endl;
    }
    std::cout << std::endl;

    // now sort by string length

    std::ranges::sort(titles, size_compare);

    for (const auto& e : titles) {
        std::cout << e << std::endl;
    }
    std::cout << std::endl;

}

We’ll revisit this yet again when we learn about lambda functions.