position in a vector

[avimitrani]

Hi,

I have an iterator that points to an item in a vector. How do I get the item's position in the vector (its distance from vec.begin() )?

Thanks,
Avi.

[D_C]

Does this help Avi?

  vector<unsigned int>::iterator it;
  for(it = vec.begin(); it != vec.end(); it++)
    cout << it-vec.begin() << " " << *it << " " << vec.end()-it << endl;

[avimitrani]

Looping over the vector may be costly. I'm looking for an 'arithmetic' calculation.

are the last two lines correct?:

vector<int> vec
// Here vec is filled...
vector<int>::iterator p;
// Here p is made to point to an element of vec...

vector <int>::difference_type position;
position = p - vec.begin()

Thanks,
Avi.

[vmohanaraj]

You can use the distance function provided for this purpose in STL. See the following example.

#include <iostream>
#include <vector>


int main() {
std::vector<int> v;
v.push_back(0);
v.push_back(1);
v.push_back(2);
v.push_back(3);

std::vector<int>::const_iterator i1, i2;

i1 = v.begin();

i2 = i1+2;
std::cout << distance(i1, i2);
}

The output for this would be 2.

[avimitrani]

Thank you, vmohanaraj.
This is what I was looking for.