one line assert to test if STL container is sorted

Question

Is there a way to write a one line condition that would return true if STL container is sorted? The container in question is std::vector

I intend to use it in an assert<

Answer 1

Use adjacent_find in combination with less or greater functor.

Restriction:
You should know whether the container is sorted in ascending or descending.

If the vector is supposed to be sorted in ascending order:

//Checks the first element where adjacent value where elem > nextElem
//returns end if the vector is sorted!
//Complexity is O(n)
vector<int>::iterator pos =  std::adjacent_find (aVec.begin(), aVec.end(),   // range
                                     std::greater<int>());               


if (pos == aVec.end()) 
{
    std::cout<<" sorted"<<endl;
}
else
{
    std::cout<<"Not sorted"<<endl;
}

Answer 2

You can use std::is_sorted(vec.begin(),vec.end()) to test if it is sorted. Note, though, that this is O(n).

Answer 3

It depends what STL data type you want to use.

A map is already sorted by the key provided the key has overloaded compare operators. You're good to go here.

A list requires that you explicitly call the sort function. You will need to keep track of whether or not you sorted it yet.

Hope this helps.