CODEWITHSUNDEEP
c++stdstdvectorpush-back
clearscreen
clearscreen

Reputation: 2027

std::vector's push_back() causing a strange compile-time error message

My snippet of code:

void
RMWavefrontFileImporter::loadVertexIntoVector(
    const std::vector<std:string> lineElements,
    std::vector<const RM3DVertex>* vertices)
{
    assert(vertices);

    std::unique_ptr<const RM3DVertex> verticeRef = verticeWithElements(lineElements);

    const RM3DVertex* vertex = vertexRef.get();
    assert(vertex);

    vertices->push_back(*vertex);
}

The error message I'm getting:

Cannot initialize a parameter of type 'void *' with an lvalue of type 'const RM3DVertice *'

I'm failing to see the problem. Is there anything obvious I'm missing?

Upvotes: 2

Views: 493

Answers (1)

Dietmar K&#252;hl
Dietmar K&#252;hl

Reputation: 153800

The value type T of a std::vector<T> needs to be CopyInsertible or MoveInsertible. To be either, it is necessary to call the moral equivalent of

T* tptr = <allocate-memory-over-here-and-make-it-look-like-a-T*>
new(tptr) T(std::forward<Args>(args);

With T being a const type this doesn't work, e.g., because there is no conversion from T* to void* if T is of the form X const. You want to remove the const from std::vector<const RM3DVertice>.

Upvotes: 6

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