Aleksandr Tukallo Aleksandr Tukallo - 1 month ago 29
C++ Question

Shared ptr in union

I want to access shared ptr, which is in union, though segmentation fault happens:

struct union_tmp
{
union_tmp()
{}
~union_tmp()
{}
union
{
int a;
std::shared_ptr<std::vector<int>> ptr;
};
};

int main()
{
union_tmp b;
std::shared_ptr<std::vector<int>> tmp(new std::vector<int>);
b.ptr = tmp; //here segmentation fault happens
return 0;
}


What is the reason of an error and how can I avoid it?

Answer

You need to initialize the std::shared_ptr inside the union:

union_tmp()
: ptr{} // <--
{}

Otherwise, ptr remains uninitialized, and calling its assignment operator triggers undefined behaviour.

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