Find max/min value of a member class in a container

Question

I have a vector/container of classes and I want to find the element that has the max/min value of a specific member; for example:

#include <vector>

struct A {
    int val;
};

int main() {
    std::vector<A> v{{1},{2},{3}};

    // how do I find the maximum of .val inside the vector?
}

Is there an "STL" way to find the item without explicitly iterating over the container and compare the values?

A comment on the two solutions

I'll add here a solution based on @Jarod42 comment on the accepted solution, based on std::ranges::less{}:

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

struct A {
    int val1;
    int val2;
};

int main()
{
    std::vector<A> v{{6,8}, {4,10}, {5,12}};

    // How can I find out the minimum and maximum?
    const auto [min, max] = std::ranges::minmax_element(v, std::ranges::less{}, &A::val1);
    std::cout << "Minimum Number: " << min->val1 << '\n';
    std::cout << "Maximum Number: " << max->val1 << '\n';
}

I prefer this solution when the comparison to determine the min/max value is trivial, while the accepted solution is more generic and can be used when the definition of "less than" is complex.

Not sure if it needs C++20's ranges, but I'm using C++20 anyway so for the moment I won't investigate it any further.

Answer 1

There are various ways:

• std::min
• std::min_element

For example:

auto smallest = std::min_element(v.begin(), v.end(), [](const A v1, const A v2) {
      return v1.val < v2.val;
});
    
std::cout << "Smallest: " << smallest->val << "\n";