使用 std::vector 创建自定义复数 class 的向量

Question

I am new to coding and currently learning C++ to get started, so please excuse my narrow knowledge and very possible mistakes in code and general C++ lingo.

I have written a class of complex numbers called ComplexNumber with member variables being double re and double im with the obvious meanings. This class has a constructor, an empty constructor, a copy constructor, a destructor etc.

Using this I am now meaning to write a class ComplexVector of vectors with entries from ComplexNumber . For now I have defined the member variables to be a vector std::vector<ComplexNumber> vec and a size int size . Additionally I would like to define a member function void print() , again with the obvious meaning. The code I have so far is:

#include <iostream>
#include <vector>

#include "complex.h"

class ComplexVector {
  private:
    std::vector<ComplexNumber> vec;
    int size;

  public:
    ComplexVector(std::vector<ComplexNumber> vector, int n){ //constructor
      size = n;
      vec = vector;
    };
    ComplexVector(){ //empty constructor
      size = 0;
      vec = {};
    };
    void print() const;
    ~ComplexVector(); //destructor
    ComplexVector(const ComplexVector& v); //copy constructor
    ComplexVector addition(ComplexVector w);      //
    ComplexVector subtraction(ComplexVector w);   // i am not worrying about these for now
    ComplexVector scale(ComplexNumber z);         //
};

with defnitions

void ComplexVector::print() const {
  for(std::vector<ComplexNumber>::iterator it = vec.begin(); it != vec.end(); it++){
    std::cout << *it << " ";
  };
  std::cout << std::endl;
};

ComplexVector::~ComplexVector(){
  std::cout << "calling destructor" << std::endl;
};

ComplexVector::ComplexVector(const ComplexVector& v){
  size = v.size;
  vec = v.vec;
};

Here is where I am getting a compiling error: in the definition of the print my compiler tells me

error: no viable conversion from '__wrap_iter<std::__1::vector<ComplexNumber, std::__1::allocator<ComplexNumber>
      >::const_pointer>' to '__wrap_iter<std::__1::vector<ComplexNumber, std::__1::allocator<ComplexNumber> >::pointer>'
  for(std::vector<ComplexNumber>::iterator it = vec.begin(); it != vec.end(); it++){

which I am not quite sure how to deal with. I have read something about certain member functions having to be defined for ComplexNumber to be used in an std::vector . I also played around with defining iterators inside of ComplexVector but this did not solve the problem. From my (to be fair very narrow) perspective there should be an iterator for vec and also corresponding begin() and end() functions. I have checked if I am passing arguments of the right type a thousand times, but I must be overlooking something.

One more thing to note is that I am very much aware that this is probably an extremely inefficient way to define a class like this. I have looked at multiple examples which used pointers to an array as the main member variable. I am surely going to implement something of that type next, but for now I want to understand where the mistake in my current code is. So thanks in advance for any answers.

One side question: I don't think I have understood the concept of a destructor very well (to be fair I haven't spent much time reading about it yet), but if anyone has a quick intuition about them, which he/she wants to share, that would be highly appreciated.

Also if you have any comments on style and/or other improvements of my code, I would appreciate it if you could share them.

Thank you!

Edit: Here is the ComplexNumber class

class ComplexNumber {
  private:
    double re;
    double im;
  public:
    ComplexNumber(double x, double y){
      re = x;
      im = y;
    };
    ComplexNumber(){
      re = im = 0;
    };
    ComplexNumber(const ComplexNumber& z);
    void print() const;
};

and definitions

void ComplexNumber::print() const {
    if(im > 0){
      std::cout << re << "+" << im << "i" << std::endl;
    } else if(im < 0){
      std::cout << re << im << "i" << std::endl;
    } else {
      std::cout << re << std::endl;
    };
};

ComplexNumber::ComplexNumber(const ComplexNumber& z){
  re = z.re;
  im = z.im;
};

And a main method:

int main() {

  std::vector<ComplexNumber> v1 = {ComplexNumber(1,2), ComplexNumber(4,2)};
  int n = 2;
  ComplexVector w1(v1,n);
  w1.print();

  return 0;
}

Answer 1

Your problem is here:

void ComplexVector::print() const {
  for(std::vector<ComplexNumber>::iterator it = vec.begin(); it != vec.end(); it++){
    std::cout << *it << " ";
  };
  std::cout << std::endl;
};

Notice that the function is marked const . This means any members of the class are treated as const qualified inside the method (ie you are not allowed to modify them). Thus when you call vec.begin() you are calling the const version of begin() on vector. This returns const_iterator not an iterator .

  std::vector<ComplexNumber>::iterator it = vec.begin()
                              ^^^^^^^^ should be const_iterator

A better way to solve this is to use auto and let the compiler work out the correct type:

   auto it = vec.begin()

So the function becomes:

void ComplexVector::print() const {
  for(std::vector<ComplexNumber>::const_iterator it = vec.begin(); it != vec.end(); it++){
    std::cout << *it << " ";
  };
  std::cout << std::endl;
}

or with auto:

void ComplexVector::print() const {
  for(auto it = vec.begin(); it != vec.end(); it++){
    std::cout << *it << " ";
  };
  std::cout << std::endl;
}

or you can improve this by using the new version of for()

void ComplexVector::print() const {
  for(auto const& item: vec){
    std::cout << item << " ";
  };
  std::cout << "\n";
}

Note: When your code works. You can ask for a review on style at https://codereview.stackexchange.com

---

Follow up based on comments: Try:

class ComplexNumber
{
     ...... 
     friend std::ostream& operator<<(std::ostream& str, ComplexNumber const& data) {
         data.print(); // You want to change this
                      // so you can pass the stream to print.
         return str;
     }
}