how to check a value exists in a c++ stl vector and apply a function to every element of the vector?

Question

I have two questions related to the vector class of the standard library in C++.

1. How can I check whether a value (let's say of an integer) already exists in a vector?

   What I want in words is as follows: "if the integer already exists in the vector, next one, else add it at the end of the vector."

2. How do I apply a function that holds arguments to every element in the vector? (It seems I can't do that with for_each)

   In words: "for each z element in the vector apply MyAddFn(i,j)"

... or maybe I'm not on the right track with the stl vector sequence container, and I should define my own iterator?

Answer 1

1)

std::find(v.begin(), v.end(), 5) == v.end() // checks that vector<int> v has no value 5.

2) Use new C++11 std::bind for example, but for real advice i need more context of use MyAddFn.

Answer 2

For 1, use std::find algorithm. If the element does not exist, it returns the iterator to the end. In that case, add the element.

Answer 3

2nd question. You can use object instead of function:

#include <vector>
#include <algorithm>

class apply_me
{
  int multiplicator_;
  public:
  apply_me(const int multiplicator) : multiplicator_(multiplicator)
  {};
  int operator ()(const int element) const
  {
    return element*multiplicator_;
  };
};
int main()
{
  std::vector<int> v;
  std::transform(v.begin(), v.end(),v.begin(), apply_me(3));
}