Finding max_element of a vector where a member is used to decide if its the maximum

Question

Consider a class A having a member x and a std::vector< A >. Now its a common task to search for the maximal x among all elements inside the vector. Clearly I can only use std::max_element if there is an iterator on the x's. But I must write one by my own, or I just make a simple for loop.

maxSoFar = -std::numeric_limits< double >::max();
for( std::vector< A >::const_iterator cit = as.begin(); cit != as.end(); ++cit )
{
  if( cit->x > maxSoFar )
    maxSoFar = cit->x;
}

but it's so tedious, and I am so lazy.. Is there a better option?

Answer 1

You can pass a comparator to max_element. And if your compiler supports lambdas(it probably does), this is easy:

std::max_element(as.begin(), as.end(),
    [](A a, A b){ return a.x < b.x; });