Finding an iterator corresponding to an object stored in a vector

Question

I have a vector v containing objects of type structure say A. Now I need to find the iterator for a particular object stored in this vector. eg:

  struct a
    {
    };
    vector<a> v;
    struct temp;  //initialized

Now if I will use

find(v.begin(),v.end(), temp);

then compiler generates error saying no match for operator '==' .

Any workaround for getting an iterator corresponding to an object in a vector?

Answer 1

You have to provide either a bool operator==(const a& lhs, const a& rhs) equality operator for your class, or pass a comparison functor to std::find_if :

struct FindHelper
{
  FindHelper(const a& elem) : elem_(elem) {}
  bool operator()(const a& obj) const
  {
  // implement equality logic here using elem_ and obj
  }
  const a& elem_;
};

vector<a> v;
a temp;
auto it = std::find_if(v.begin(), v.end(), FindHelper(temp));

Alternatively, in c++11 you can use a lambda function instead of the functor.

auto it = std::find_if(v.begin(), v.end(),  
                       [&temp](const a& elem) { /* implement logic here */ });