Question

I’m trying to use stl sort() in a class function. I would like to sort an array of structs that look like this:

struct foo{
    double num;
    std::string s;
};

with a comparison function like this:

bool aGreaterThanb(foo a, foo b){
    if (a.num > b.num){
        if(a.num == b.num){
            if (anotherOutsideComparison(a.s, b.s)){
                return true;
            }
        }
        else
            return true;
    }
    else
        return false;
}

But I’m not sure how I can format this to get it to compile. How should I format this so I can call sort(fooarray[0], fooarray[end], aGreaterThanb);? (An example would be great)

Answer 1

It works just as you want already:

#include <algorithm>
int main()
{
    foo     data[10];
    std::sort(&data[0], &data[10], aGreaterThanb);
}

But you have syntax error. You are missing a brace:

        return true;
} // <--- Missing this line
else
    return false;

For efficiency you should pass by const reference:

bool aGreaterThanb(foo const& a, foo const& b){