push_back crashed when using std::vector if the type only defined copy constructor with c++11

Question

The code like this:

#include <iostream>
#include <vector>

struct Foo
{
    int i;
    double d;
};

class Boo
{
public:
    Boo() : fptr(nullptr) 
    {
        std::cout << "Boo default construct..." << std::endl;
    }
    Boo(int i, double d):fptr(new Foo{i,d})
    {
    }

    Boo(const Boo &rhs) :fptr(new Foo{rhs.fptr->i,rhs.fptr->d})
    {
    }

    Foo *fptr;
};

int main(int argc, char const *argv[])
{
    std::vector<Boo> vec(1);
    Boo b(42, 10.24);
    vec.push_back(b);
    return 0;
}

Env: Ubuntu 16.4 LTS with gcc 5.4 g++ -std=c++11 test.cpp -o test -g

./test

If define move constructor,this will work good. I debuged it several hours but can not found what's wrong with it, maybe because some rules in c++ 11 that i did't know.

Could somebody help me? Thanks!

Answer 1

Your Boo copy constructor derefernces a pointer fptr that may be null.

A std::vector::push_back may reallocate vector storage. Reallocating may use copy constructors.

That is what is happening in your program. You are copying a Boo that has a null pointer.