SL Algorithms

We looked at some of the algorithms that work on standard C++ containers (like vectors) previously. Now we can look at some more.

Consider std::sort()—you can provide a function to sort that tells it how to do the comparison.

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 45 algorithms_functions.cpp

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

bool size_compare(const std::string& a, const std::string& b);

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::sort(titles.begin(), titles.end());

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

    // now sort by string length

    std::sort(titles.begin(), titles.end(), size_compare);

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

}

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

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