How do I return a vector object from a function?

Question

I'm trying to get this function to create a new object but I can't get it working.

Main.cpp:

BaseUnit MyUnits;
vector<BaseUnit> Units;
MyUnits.CreateNewUnit(Units);

BaseUnit.cpp:

BaseUnit::BaseUnit(int ID)
{
    UnitID = ID;
}

..Other code...

void BaseUnit::CreateNewUnit(vector<BaseUnit> MyVector)
{
    UnitID++;
    BaseUnit NewUnit(UnitID);
    MyVector.push_back(NewUnit);

}

I don't know how to get it to return back into the Vector of object in the main code.

You may see here how to use a vector as return type. For your case you'll need a reference parameter: void BaseUnit::CreateNewUnit(vector<BaseUnit>& MyVector) — πάντα ῥεῖ
– πάντα ῥεῖ, Commented Apr 11, 2015 at 11:35
To make your code easier to understand for others, consider to adhere to established naming conventions. For C++ that means that only types, macros and constants should start with uppercase letters. — das-g
– das-g, Commented Apr 11, 2015 at 12:01

das-g · Accepted Answer · 2015-04-11 13:03:39Z

1

To return the modified vector

vector<BaseUnit> BaseUnit::CreateNewUnit(vector<BaseUnit> MyVector) // note the return type
{
    UnitID++;
    BaseUnit NewUnit(UnitID);
    MyVector.push_back(NewUnit);
    return MyVector; // simple as that
}

You can then use this function to update the original vector:

Units = MyUnits.CreateNewUnit(Units);

However, this will modify a copy of the vector and then change the variable Units to refer to that new vector (in C++11) or even create another copy of it and assign that (in C++98), which both isn't very efficient. To instead directly modify the passed vector in your function, pass it as reference like πάντα ῥεῖ suggested in the comments:

void BaseUnit::CreateNewUnit(vector<BaseUnit>& MyVector) // note the '&'
{
    UnitID++;
    BaseUnit NewUnit(UnitID);
    MyVector.push_back(NewUnit); // this will now modify the original vector
}

Use this with

MyUnits.CreateNewUnit(Units);

as you had in your original code.

edited Apr 11, 2015 at 13:03

answered Apr 11, 2015 at 11:52

das-g

10.1k6 gold badges44 silver badges95 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

celtschk Over a year ago

"However, this will modify a copy of the vector and then change the variable Units to refer to that new vector" That's only in C++11; in C++ versions before C++11, there will be a second copy made in the assignment of Units. Note that g++ (and possibly other compilers) still defaults to older C++ versions.

das-g Over a year ago

Good catch, @celtschk, I wasn't aware of that. I've edited my answer to reflect that.

Collectives™ on Stack Overflow

How do I return a vector object from a function?

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related