CODEWITHSUNDEEP
c++objectreferencereturnstack
TJ8
TJ8

Reputation: 121

Is the following code returning a reference to a stack object or is it valid?

I have this code which calls a function in the current process from a DLL that returns the value by reference. One person I talk to says it is correct and another states that it is returning a reference to a stack object and that it is undefined behaviour. I am unsure which person is more factual as I don't have as much experience as either of them.

// Function call inside of the current process at a specific address. 
// Returns a matrix from the given meshcomponent and an id
FMatrix* GetMatrix(MeshComponent* mesh, FMatrix* result, int id) {
    return reinterpret_cast<FMatrix*(__fastcall*)(MeshComponent*, FMatrix*, int)>(address)(mesh, result, id);
}

// Gets the wanted 3D Vector out of the Matrix
void GetLocation(MeshComponent* mesh, FVector* result, int id) {
    FMatrix matrix;
    GetMatrix(mesh, &matrix, id);  <-- // When the function ends, is it possible for other stack operations to overwrite the matrix? Or is this valid?
    *result = static_cast<FVector>(matrix.WPlane);
}

// Usage, running from a DLL inside the process:
...
FVector location;
GetLocation(mesh, &location, id);
...

The code as it is does work, but if it is truly returning a reference to a stack object, I know that could break at any point and I will change it accordingly.

Upvotes: 0

Views: 74

Answers (1)

Yola
Yola

Reputation: 19093

According to your comment

FVector is just a struct of a 3D Vector containing {x, y, z}

this line copies data to a location pointed by result

*result = static_cast<FVector>(matrix.WPlane);

There is no returning by reference. Example for this would be

int& foo() {
    static int i;
    return i;
}

Upvotes: 1

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