Question

Question is about sorting std::vector<myclass> using function sort from STL’s algorithms class.
Standard way is : sort(v.begin(), v.end(), &myfunct)
where myfunct is:

bool myfunct( myclass first, myclass second ) {   
    if (first.value < second.value)   
        return true;   
    else return false;   
}

Approach above takes more than one line. I am curious how to do it in one line. Is it possible define function that compares myclass objects inside sort function? May be somehow use this (a < b) ? a : b. I remember that there is something like this in C#, but I forgot how is it called. Is it possible to do in C++.

Answer 1

First, you can just return first.value < second.value but this doesn’t get rid of the function. In C++2011 you can use a lambda function:

   std::sort(begin, end, [](myclass const& f, myclass const& s){ return f.value < s.value; });

Without C++2011 I think you’ll need a function object because there isn’t anything which projects your class to the value you actually want to compare.

BTW, you definitely want to pass everything but the most trivial objects by reference to your comparison function.