how do i declare a function with return type vector?

[jinjin12]

how do i declare a function that returns a vector?

[sammy34]

Can you pass it in as a reference parameter instead?

EDIT: Sorry, just saw the other post, http://www.cplusplus.com/forum/beginner/21957/

[jinjin12]

yea that's what i did, but i was just wondering if you could make a function with return type vector, cause it will make my project easier.

[sammy34]

You could, but I think we'd all suggest against it.

vector<int> ReturnVect()
{
	vector<int> myVect(10);

	myVect.push_back(5); // Do stuff...

	return myVect;
}

Repeat: This is not a good way to do it. It has performance implications involved with copying, the same as were mentioned in the other thread. In addition, you're getting a copy of the vector returned, not the original one.

[jsmith]

I would not necessarily suggest against it.

The above is convenient in that it requires only one line of code to call:

vector<int> v = ReturnVect();

which lends itself well to more functional programming. For example:

PrintVect( ReturnVect() );

Returning the vector via reference parameter is annoying because then I have
to write two lines:

vector<int> v;
ReturnVect( v );

I would advocate using the return value of the function to return the container
unless it is proven to be a performance bottleneck.

[tummychow]

It's more "traditional" to pass vectors and other containers by a pair of iterators to them. But returning a vector is generally fine. Of course, it will be, as sammy noted, inefficient in terms of the whole copying business. But chances are, it'll be fine for most programs.

[sammy34]

@jsmith and tummychow: Fair call, thanks for your input. I've been doing real-time embedded programming recently, so I guess I'm always considering efficiency as a high priority.

[tummychow]

Generally, I actually do agree with you. Just because of the copy overhead (which could be a problem in the future and almost never will be an advantage), I would advise against copying vectors. What happens if you've got some vector containing thousands of elements? (I can't imagine any such situation, but then again, I program for fun, not for corporate purposes.) But it's... livable. I'd prefer to pass by reference or iterator pair in most cases personally though.

[jinjin12]

thanks guys, its cool to know that i can do this. however i did not know that it would return a copy of a vector. i guess i'lll just be passing by ref then, since it is more efficient cause the vector i want is pretty big in size.

just a side question, so anytime i return a value from function, it returns not the value itself but a copy of the value? it is possible to return a reference to that value isn't of a copy? cause i mean u can pass by ref so returning by ref seems plausible to me.