UB in member-variable reference

[high sierra]

Hey guys, thanks for all the help thus far. Let's tackle this one.

Here is my struct I'm trying to create:

    struct Map {
        int32_t width;
        int32_t height;

        std::vector<Coordinate> map;

        Coordinate& sPos;
        Coordinate& ePos;
    };

And here is the function that creates the struct:

    Map parse_input(std::istream& stream) {
        std::vector<Coordinate> map; 
        int32_t height = 0;
        int32_t width = 0;

        Coordinate sPos;
        Coordinate ePos;

        for(std::string line; std::getline(stream, line); ) {
            std::istringstream iss(line);
            char temp;
            width = 0;
            while(iss >> temp) {
                if(temp == 'S') {
                    sPos = Coordinate{ width, height, 0, temp };
                    map.push_back(Coordinate{ width, height, 0, temp });
                }
                else if(temp == 'E') {
                    ePos = Coordinate{ width, height, 100, temp };
                    map.push_back(Coordinate{ width, height, 100, temp });
                } else {
                    map.push_back(Coordinate{ width, height, temp-'a', temp });
                }
                width++;
            }
            height++;
        }

        auto& test = map[(sPos.y * height) + sPos.x];
        auto value = (sPos.y * height) + sPos.x;
        return Map{ width, height, map, test, map[(ePos.y * height) + ePos.x] };
    }

The goal here is that I want to create my struct in place in the return with references to those objects in the map vector. REMEMBER map is not a <map> it is a VECTOR!!!!

For some fucking reason, after the return Map, the object after inspection has a correct reference to ePos but some random fucking UB data for sPos. Guess what? test returns the correct reference, value evaluates to 0. How the fuck can ePos work and not sPos?

[rich adder]

When your question is answered use !solved to mark the question as resolved.

Remember to ask specific questions, provide necessary details, and reduce your question to its simplest form. For tips on how to ask a good question run !howto ask.

[jolly spoke]

does it work if you get rid of auto& test?

[high sierra]

no, I did that to ensure that the map[selectionCalculation] actually returns the correct object

It's weird because ePos reference works fine... just not sPos

it's really odd

[sour wind]

you are returning a struct that contains references to elements of a local vector

[high sierra]

I want to know why

[sour wind]

that vector is destroyed the moment your function returns

[high sierra]

but that local vector is passed to the struct

by value

[sour wind]

you are making a copy

[high sierra]

Ok, so my references are broken then?

[sour wind]

the references do not refer to elements of that copy

[high sierra]

Why is it that ePos still works

ePos will work, it points to the right object everytime

[sour wind]

you can std::move the vector into your Map

that'll probably fix the problem unless i'm overlooking something

[jolly spoke]

yeah it does fix it

you just have to create the references to the map before you move it

[high sierra]

Ok, I need to jet here to poop, but I will try when I get back

thanks guys

[rich adder]

@high sierra Has your question been resolved? If so, run !solved :)

[sour wind]

np ^^

[high sierra]

What does that look like?

I'm doing std::move(map) in the initialization list

and it now breaks my sPos and ePos in the list \

it moves the values though

[sour wind]

wdym?

[high sierra]

nvm I got it working

my b

[sour wind]

k^^

[rich adder]

This question thread is being automatically closed. If your question is not answered feel free to bump the post or re-ask. Take a look at !howto ask for tips on improving your question.