I have a function what creates a vector, does somthing with it and then return it as an rvalue using std::move.
When I am assigning it to a variable, I’m expecting to call std::vector‘s move constructor std::vector::vector(vector&&).
But I’m getting a segmentation fault.

Here’s my code:

#include <iostream>
#include <vector>

std::vector<int>&& getVector(int start)
{
    auto result = std::vector<int>();
    result.reserve(10);
    for (int i = start; i < start + 10; i++)
        result.push_back(i);
    return std::move(result);
}

int main()
{
    std::cout << "Did I break here 1" << std::endl;
    auto vec = getVector(10);
    std::cout << "Did I break here 2" << std::endl;
}

It gives me

Did I break here 1
[1]    55419 segmentation fault <executable_file>

I just guessing there’s someting wrong with the move constructor or the rvalues. Btw I return an rvalue to not copy the vector’s value an steal the pointer to it.

>Solution :

You are returning a reference to the local variable result. That object is destroyed before the function returns and you are then trying to move-construct vec from a dangling reference.

You do not need to return-by-rvalue-reference or to std::move explicitly in a return statement to get move semantics. You should just do the straight-forward thing:

std::vector<int> getVector(int start)
{
    auto result = std::vector<int>();
    //...
    return result;
}

//...

auto vec = getVector(10);

Now vec will be move-constructed from result and the constructor call may even be elided. Before C++17 there may be three (including = std::vector<int>()) move constructor calls if the compiler is not optimizing. Since C++17 there will only be one at most. In any case there will not be any copy constructor calls.