CODEWITHSUNDEEP
c++set-intersection
Elliott
Elliott

Reputation: 2623

std::set_intersection with custom comparator

I'm trying to understand the syntax for std::set_intersection when using a custom comparator. I'm trying to get the intersection of sets one and two, which should result in a set (intersect) containing only element f2.

I get error:

passing ‘const Foo’ as ‘this’ argument discards qualifiers

#include <set>
#include <string>

struct Foo
{
    std::string str;
};

struct Compare_custom
{
    bool operator () (const Foo & lhs, const Foo & rhs)
    {
        return (lhs.str.size() > rhs.str.size());
    }
};

int main ()
{
    std::set<Foo, Compare_custom> one, two, intersect;

    Foo f1, f2, f3;

    f1.str = "-";
    f2.str = "--";
    f3.str = "---";

    one.insert(f1);
    one.insert(f2);

    two.insert(f2);
    two.insert(f3);

    std::set_intersection(one.begin(), one.end(),
        two.begin(), two.end(),
        intersect.begin(), Compare_custom());
}

What am I doing wrong?

Upvotes: 2

Views: 795

Answers (1)

HMD
HMD

Reputation: 2226

You are using std::set_intersection wrongly for std::set. Try this :

std::set_intersection(one.begin(), one.end(),
        two.begin(), two.end(),
        std::inserter(intersect, intersect.begin()), Compare_custom());

Upvotes: 3

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