STL algorithms in C++

sort, find, count_if, accumulate, transform and friends, and why algorithms beat hand-written loops.

<algorithm> and <numeric> hold dozens of tested building blocks that work on any range:

std::sort, std::stable_sort
std::find, std::find_if, std::count_if, std::any_of
std::accumulate (sum or fold), std::transform (map)
std::lower_bound (binary search on sorted data)
std::erase_if (C++20) to remove matching elements

Using a named algorithm says what the code does, and avoids off-by-one mistakes. C++20 ranges let you pass the container directly: std::ranges::sort(v).

Example

#include <algorithm>
#include <iostream>
#include <numeric>
#include <vector>

int main() {
    std::vector<int> v{4, 8, 15, 16, 23, 42};
    int total = std::accumulate(v.begin(), v.end(), 0);
    bool has_odd = std::any_of(v.begin(), v.end(), [](int x) { return x % 2 != 0; });
    std::erase_if(v, [](int x) { return x > 20; });
    std::cout << total << " " << has_odd << " " << v.size() << "\n";
    return 0;
}

Output:

108 1 4

STL algorithms in C++

Example

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