Changing target of pointer in function (to a dynamically created object)

Question

That may well be silly, but I'm going crazy here ..

Why does pTest doesnt point on the new int after test function in main ? It causes seg fault. And how can I do it.

In my real code I need to pass a pointer and dynamically create the object because pTest is a subclass of a virtual class (reading from file so I don't know in advance)

void test(int* pTest)
{
    int *p = new int(2);
    pTest = p;
    std::cout << "pTest : " << *pTest << std::endl;
    return;
}

int main()
{
  int *pTest = NULL;
  test(pTest);
  std::cout << "pTest : " << *pTest << std::endl;

  return 0;
}

I swear there's *at least* one question precisely like this every day... — Kerrek SB, Oct 29 '13 at 14:30
Thank you very much, didn't think of searching. I bet the ones asking for it everyday also had a hard time coming with a title for their question. — user2287453, Oct 29 '13 at 14:35
possible duplicate of [How do I use arrays in C++?](http://stackoverflow.com/questions/4810664/how-do-i-use-arrays-in-c) — Joel Falcou, Mar 06 '14 at 09:50
possible duplicate of [Difference between value parameter and reference parameter?](http://stackoverflow.com/questions/2207179/difference-between-value-parameter-and-reference-parameter) — Tadeusz Kopec for Ukraine, Mar 06 '14 at 14:00

score 2 · Answer 1 · answered Oct 29 '13 at 14:37

2

If you want to mutate value passed as a parameter you have to provide pointer to it. That means if you want to change value of a given int you are passing int* . In your case you want to mutate int* so that you need to pass it as int** instead.

answered Oct 29 '13 at 14:37

MarekR

2,410
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score 1 · Accepted Answer · answered Oct 29 '13 at 14:34

1

you need to pass pTest by reference: void test(int*& pTest) if you want the pTest value to be altered outside the scope of this function.

void test(int*& pTest)
{
    int *p = new int(2);
    pTest = p;
    std::cout << "pTest : " << *pTest << std::endl;
    return;
}

answered Oct 29 '13 at 14:34

Stephane Rolland

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1

And instead of providing one of the million dubplicates, that I can't find because I don't know what to search for you make a comment about him not doing so.. – user2287453 Oct 29 '13 at 14:50

Changing target of pointer in function (to a dynamically created object)

2 Answers2