Question

• I have a vector of custom Struct that needs to be sorted on different criteria each time
• Implementing operator < will allow only one criteria
• But I want to be able to specify sorting criteria each time I call C++ standard sort.

How to do that?

• Please note it is better to be efficient in running time..

Thanks

Answer 1

You can define what comparison function to use in each run of the sort algorithm by using the third argument:

template <class RandomAccessIterator, class StrictWeakOrdering>
void sort(RandomAccessIterator first, RandomAccessIterator last,
          StrictWeakOrdering comp);

A simple example:

struct person {
   std::string name;
   int age;
};
bool sort_by_name( const person & lhs, const person & rhs )
{
   return lhs.name < rhs.name;
}
bool sort_by_age( const person & lhs, const person & rhs )
{
   return lhs.age < rhs.age;
}
int main() {
   std::vector<person> people;
   // fill in the vector
   std::sort( people.begin(), people.end(), sort_by_name );
   std::sort( people.begin(), people.end(), sort_by_age );
}