Question

I’m interested in:

• having an std::vector of pointers to an user defined type/class
• filling this vector in the fastest way

I would like to solve this with:

• while + iterators ( a non-C++11 solution )
• for_each iteration + lambda ( a c++11 solution )

Now after reading the documentation I was trying this for the iterator part with the while

#include <iostream>
#include <vector>

class A{
  public:
    A(){}
    ~A(){}
  private:
    int n;
    double d;
    float f;
    std::string s;
};

int main(){
  std::vector<A*> v(100); // fixed *A to A*
  std::vector<A*>::iterator iter = v.begin(); // fixed *A to A*
  while( iter != v.end() )
  {
    *iter = new A(); // iter = A(); by the way this does not works either // now fixed using new
    ++iter;
  }
  return(0);
}

i know that this is trivial but to me it’s not, in my understanding iter it’s a pointer and needs to be indirected to the real value that it is pointing in the vector; clearly this concept doesn’t work this way.

With the lambda and the for_each i just don’t get how to use a constructor for a custom defined class because the documentation only talks about generic methods and functions and seems like i can’t use a constructor.

How i can build an object with iterators and lambdas ?

Also, there is a faster way to cycle the entire vector when i need to perform the same action all over the place without using the iteration approach with the while and the for_each or the for.

I would like to avoid the copy constructor overhead so i would like to keep all possible solutions using pointers.

Thanks.

Answer 1

First you should use A* instead of *A to create pointers in C++ and second you can’t set a pointer to an instance that created in stack using A() instead you should create the value on the heap or use address of a variable from stack, so you should have *iter = new A()