creating vector with constructor parameter in c++

Question

Im trying to create 2 vectors of 5 objects (Cats) with a constructor parameter (color).

But i cant find the right syntax.

#include <iostream>
#include <bits/stdc++.h>

using namespace std;

class Cats{
Cats(string color);

};

Cats::Cats(string color){
cout << "Cat " << color << " created" << endl;
}

int main()
{
  vector<Cats> blacks (5, "black");
  vector<Cats> whites (5, "white");
}

I want the string of each cat with the color i write to the constructor.

[Why should I not #include ?](https://stackoverflow.com/questions/31816095/why-should-i-not-include-bits-stdc-h) — πάντα ῥεῖ, Aug 04 '19 at 07:32

HolyBlackCat · Accepted Answer · 2019-08-04T07:41:53.720

2

You want vector<Cats> blacks(5, Cats("black"));.

Also see Why should I not #include <bits/stdc++.h>?

edited Aug 04 '19 at 07:41

answered Aug 04 '19 at 07:29

HolyBlackCat

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4

`vector blacks(5, string("black"));` would also work. – john Aug 04 '19 at 07:31
why does the constructor runs only ONE time with each vector? – Pablo Lopez Aug 04 '19 at 08:02
2

@PabloLopez Because five `Cats` are created using the copy constructor, from that single `Cats` you constructed manually. – HolyBlackCat Aug 04 '19 at 08:50
ok, but how i get the constructor to work for each time? meaning: i will like to show every time a cat is created (cout ...) – Pablo Lopez Aug 04 '19 at 08:52
2

@PabloLopez Provide a custom copy constructor: `Cats(const Cats &other) {...}` and print something in it as well. – HolyBlackCat Aug 04 '19 at 08:57

Alan Birtles · Answer 2 · 2019-08-04T08:16:14.437

The compiler will not automatically perform two implicit conversions. Your string literal is a const char* which needs to be converted to std::string and then to Cats before it is the correct type to pass into the vector constructor.

You can help the compiler out by performing one of the conversions explicitly:

// Pass Cats to the vector constructor, compiler implicitly converts string literal to std::string
vector<Cats> blacks(5, Cats("black"));
// Pass std::string, compiler implicitly converts to Cats before calling the vector constructor
vector<Cats> whites(5, std::string("black"));

Alternatively if you're going to be calling code similar to this often, it could be simpler to add a const char* constructor to Cats:

class Cats{
Cats(string color);
Cats(const char* color)
:Cats(std::string(color))
{}
};

Your original code would then work.

creating vector with constructor parameter in c++

2 Answers2