How to reference to the longest vector without copy it from inputs C++?

Question

Suppose I have a C++ function like the following:

int foo (vector<int>& v1, vector<int>& v2){

    vector<int> long_vec;
    if ( v1.size() >= v2.size())
        long_vec = v1;
    else
        long_vec = v2;

    // do stuff with "long_vec" ...
}

I don't want to copy the contents in "v1" or "v2" into "long_vec". Instead, I just want to know whichever "v1" or "v2" is longer, and use it. I know something like the vector reference like the following:

vector<int>& long_ref = v1;

But this reference has to be initialized when declared. Basically I want the following behavior:

int foo (vector<int>& v1, vector<int>& v2){

    //vector<int> long_vec;
    vector<int>& long_vec; // won't compile

    if ( v1.size() >= v2.size())
        long_vec = v1;
    else
        long_vec = v2;

    // do stuff with "long_vec" ...
}

Is there a way to achieve this. Thank you very much.

score 2 · Accepted Answer · 2018-09-11T20:51:06.730

2

Use the conditional operator:

  vector<int> & long_vec = v1.size() > v2.size() ? v1 : v2;

edited Sep 11 '18 at 20:51

answered Sep 11 '18 at 20:49

1

you forgot the reference part – Fureeish Sep 11 '18 at 20:49
This is usually called not a conditional, but ternary operator. – SergeyA Sep 11 '18 at 20:49
1

@SergeyA Guess how the standard calls it :) Hint: It's not ternary – Rakete1111 Sep 11 '18 at 20:51
@Fureeish - Oops, typical copy and paste snafu. – Sep 11 '18 at 20:51
@Rakete1111 fine, everyone knows it as a ternary operator :) But yes, my comment was not correct. – SergeyA Sep 11 '18 at 20:52
"Ternary" just means "composed of three parts". As it's the only operator that has three operand, people call it that. But really, the name has nothing to do with the operator's function. And let's consider the case where someone came up with another useful operator that required three operands. – François Andrieux Sep 11 '18 at 20:54
@SergeyA And also, would it be useful if someone asked "how do I add two numbers together" to tell them to "use a binary operator"? – Sep 11 '18 at 20:58
I learned something today. Thank you very much – BlowMyMind Sep 11 '18 at 21:32

score 1 · Answer 2 · answered Sep 11 '18 at 20:48

1

Use a ternary operator:

int foo (vector<int>& v1, vector<int>& v2){

    vector<int>& long_vec = v2.size() > v1.size() ? v2 : v1;

    // do stuff with "long_vec" ...
}

answered Sep 11 '18 at 20:48

Fureeish

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Perfection solution to my problem. Thank you very much. – BlowMyMind Sep 11 '18 at 21:30

How to reference to the longest vector without copy it from inputs C++?

2 Answers2