Question

I have a problem while comparing the values in two vectors.

Following is the sample code of my program:

  template <typename T> bool CompareVectors(std::vector<T> vector1, std::vector<T> vector2)
  {
    std::sort(vector1.begin(),vector1.end());
    std::sort(vector2.begin(),vector2.end());
    if (vector1.size() != vector2.size())
      return false;
    else
    {
      bool found = false;
      std::vector<T>::iterator it;
      std::vector<T>::iterator it2;
      for (it = vector1.begin();it != vector1.end(); it++)
      {      
        for(it2 = vector2.begin(); it2 != vector2.end(); it2++)
        {
          if(it == it2) // here i have to check the values in the itearators are equal.
          {
            found = true;
            break;
          }
        }
        if(!found)
          return false;
        else
          found = false;
      }
      return true;  
    }
    };

In this sample code I have to compare the two vectors. For that I have sorted the two vectors using std::sort(). Since the data type in the vector is a template (I am using a class object in the vector), the std::sort() is not working properly. Ie, sometimes the two vectors give different order of elements after sorting.

So I am not able to use the std::equal() function also.

For an alternative solution, I have used two iterators for the twi vectors.

And iterating one vector and searches that element in the other vector. For this the iterator comparison is cannot be usable.

Answer 1

First you’ve to use typename keyword here:

typename std::vector<T>::iterator it;
typename std::vector<T>::iterator it2;

without typename your code wouldn’t even compile.

To compare the values pointed to by iterators, you’ve to do this:

if( *it == *it2)

---

You could write you compare function as:

//changed the name from CompareVectors() to equal()
template <typename T> 
bool equal(std::vector<T> v1, std::vector<T> v2)
{
  std::sort(v1.begin(),v1.end());
  std::sort(v2.begin(),v2.end());
  if ( v1.size() != v2.size() )
       return false;
  return std::equal(v1.begin(),v1.end(), v2.begin());
};