堆栈std ::矢量范围

Question

im new to c++ and i'm finding hard to understand some vector behaviours. I was trying to implement a function to return an array of int and i found many suggestions to use a vector like this:

vector<int> myFunc()
{
    vector<int> myVector;
    //add elements to vector here...
    return myVector;
}

But from what i know 'myVector' is an object created on the stack, so isnt it going out of scope when the function end? when does its destructor get called? I know there are few other questions about returning vectors, but i need to clarify this specific point, hoping to not have duplicated a question.

Answer 1

Yes because myVector is allocated on the stack, as soon as the function returns, it goes out of scope. But in this case that's ok! Your function signature is

vector<int> myFunc()

which returns a copy of myVector so it doesn't matter that it's going out of scope since it's already being copied for the return.

However if you changed it to something like

vector<int> & myFunc()

now your telling it not to copy myVector and you'll have a problem called a dangling reference since myVector will be destructed and you don't copy it but still try to use it.

Answer 2

Your code returns a copy of the myVector instance on the stack. So it's OK it goes out of scope and is deleted (after return).

Answer 3

It does go out of scope, but when you return a class or struct, the compiler automatically makes a copy for you, so that your receiving object is filled in with the content of the original object.

Similar to:

vector<int> a;
vector<int> b;

... fill in vector a with stuff ... 

b = a;