Create Multiple Objects in a loop c++ - c++

Question

I'm a beginner and was researching to find out if you can grab a name from an array to then put that name as the name of the object in a for loop.
The code a specifically created for this question is represented below:
#include <iostream>
using namespace std;
class YourMum{
public:
string name;
YourMum(string aName){
name = aName;
}
};
int main()
{
string names[5] = {"Jeremy_Clarkson", "Boris_Johnson", "Vladmir_Putin", "Peter_Griffin", "MeAndYourMum"};
for(int i = 0; i < 4; i++) {
YourMum names[i];
cout << names[i].name << endl;
cout << "You are great if you answer my question!";
}
return 0;
}

Answer 1

Okay, it's not clear what you're trying to do, but you've got a few things that aren't a good idea.
First, you defined string names[5] and then inside loop you hid names by making a second variable with the same name. While that's legal, it's a bad practice.
Second, you're using the second one (YourMum names) illegally:
You declared it as length i (using a non-standard feature of the compiler) but then reference element i. The elements of an array of length i range from 0..i-1, so [i] is one element past the end.
And you haven't initialized it anyway.
I'm not really clear what you're trying to do, so I can't even provide example code of how to do it.

Answer 2

The YourMum class you have shown is not default constructible, so YourMum names[size]; will not work. Every object of YourMum needs to be passed a parameter in order to create it. You can use placement-new for that, eg:
#include <iostream>
#include <type_traits>
using namespace std;
class YourMum{
public:
string name;
YourMum(string aName){
name = aName;
}
};
int main()
{
string names[5] = {"Jeremy_Clarkson", "Boris_Johnson", "Vladmir_Putin", "Peter_Griffin", "MeAndYourMum"};
std::aligned_storage<sizeof(YourMum), alignof(YourMum)>::type arr[5];
YourMum *mums = reinterpret_cast<YourMum*>(arr);
for(int i = 0; i < 5; i++) {
new (&mums[i]) YourMum(names[i]);
}
for(int i = 0; i < 5; i++) {
cout << mums[i].name << endl;
cout << "You are great if you answer my question!";
}
for(int i = 0; i < 5; i++) {
mums[i].~YourMum();
}
return 0;
}
Or, you can use std::vector instead:
#include <iostream>
#include <vector>
using namespace std;
class YourMum{
public:
string name;
YourMum(string aName){
name = aName;
}
};
int main()
{
string names[5] = {"Jeremy_Clarkson", "Boris_Johnson", "Vladmir_Putin", "Peter_Griffin", "MeAndYourMum"};
std::vector<YourMum> mums;
mums.reserve(5);
for(int i = 0; i < 5; i++) {
mums.emplace_back(names[i]);
}
for(int i = 0; i < 5; i++) {
cout << mums[i].name << endl;
cout << "You are great if you answer my question!";
}
return 0;
}

Answer 3

First of all, you should rename the name variable to something like _name or name_ for lisibility (to differenciate it from variables that aren't in the class), and you should also use the private section of your class to declare it and use getters/setters functions to edit it. Secondly, in your code you are declaring the object inside a loop, so it will get destroyed as soon as the loop iterates again, so if you want to create n objects in a loop and interact with them after you should either use a container class (like std::vector) or use a default constructor (which is better). Here is an updated version of your code:
#include <iostream>
#include <string>
class YourMum
{
public:
YourMum(void) : _name() { }
YourMum(std::string name) : _name(name) { }
std::string getName(void) const { return _name; }
void setName(std::string name) { _name = name; }
private:
std::string _name;
};
int main()
{
std::string names[5] = { "Jeremy_Clarkson", "Boris_Johnson", "Vladmir_Putin", "Peter_Griffin", "MeAndYourMum" };
YourMum mums[5];
for (int i = 0; i < 5; i++)
{
mums[i].setName(names[i]);
std::cout << mums[i].getName() << std::endl
<< "You are great if you answer my question!" << std::endl;
}
// this way you can still access mums here if you want to
return 0;
}
If you want to access to a class by it's name as index what you can also do is using std::map like this
#include <map>
int main()
{
std::string names[5] = { "Jeremy_Clarkson", "Boris_Johnson", "Vladmir_Putin", "Peter_Griffin", "MeAndYourMum" };
std::map <std::string, YourMum> mums;
for (int i = 0; i < 5; i++)
mums[names[i]] = YourMum(names[i]);
std::cout << mums["Jeremy_Clarkson"].getName() << std::endl;
return 0;
}

Answer 4

Try This
> for(int i = 0; i < 4; i++) {
> YourMum name(names[i]);
>
> cout << name.name << endl;
> cout << "You are great if you answer my question!";
> }