C++ - Return reference to a vector element

Question

I want to return a reference to a single element in a vector I get as param and then compare there memory addresses. A simplified example of my code is shown below:

const int &test(std::vector<int> i) {
    return i.at(3);
}

TEST(test, all_test) {
    const std::vector<int> i = {1,2,3,4,5};
    const int &j = test(i);
    ASSERT_THAT(&j, Eq(&i.at(3)));
}

Using this I get the following error message:

Failure
Value of: &j
Expected: is equal to 0x55da7899d4dc
  Actual: 0x55da7899d4fc (of type int const*)

How can I return reference to a single vector element?

Ivaylo Valchev · Accepted Answer · 2018-05-27 18:05:20Z

7

You're passing the vector by value so you're returning a reference to a temporary element. If you pass the vector by reference you should be fine.

edited May 27, 2018 at 18:05

Ivaylo Valchev

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answered May 27, 2018 at 18:01

Guido Niewerth

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2 Comments

Greeneco Over a year ago

Using const int &test(std::vector<int> &i) also results in a different address in the end. Could you give an working example?

user3366592 Over a year ago

Passing by reference and marking the first parameter as const (otherwise it doesn't compile, you can just make i non-const either) makes your code work as you intended.

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