Initializing a pointer in C++?

Question

So I have these statements in my code(there are many other lines but this is giving me trouble):

int *vector1;

if (vector1 == NULL)
    {

    }

When I try to run it it says "uninitialized local variable 'vector1' used" If I put "&vector1 == NULL" it doesn't complain but also doesn't work correctly.

I really don't understand why I am getting this error. I want it to do something if vector1 doesn't point to anything.

&vector1 is never null. why don't you just initialize vector1. — thang, Mar 01 '15 at 03:06

score 2 · Accepted Answer · edited May 23 '17 at 11:50

2

int *vector1 = NULL;
if (vector1 == NULL)
{

}

will work fine

int *vector1 = nullptr;
if (vector1 == nullptr)
{

}

Also works if you want to be a bit more up to date.

Pointers are not set to NULL by default. The answer why is here: Why aren't pointers initialized with NULL by default?

edited May 23 '17 at 11:50

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answered Mar 01 '15 at 03:06

marsh

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of course, that (vector1==NULL) is always true... – thang Mar 01 '15 at 03:07
Ah, that makes sense. However, I thought when pointers were created they inherently pointed to NULL? – Pongjazzle Mar 01 '15 at 03:08
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No that is not true, they will point to garbage data. I have udpated my post with a link to as why. – marsh Mar 01 '15 at 03:08

score 1 · Answer 2 · edited May 23 '17 at 11:50

1

The warning uninitialized local variable 'vector1' used tells you that you're using vector1 even though you haven't initialized it. Therefore, its value might be anything.

Pointers (non-static ones) are not default-initialized to 0. They are initialized with random junk data.

If you want to initialize it with 0, NULL, or nullptr (all the same thing):

int *vector1 = 0; // or NULL, or nullptr.

edited May 23 '17 at 11:50

Community

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answered Mar 01 '15 at 03:09

Emil Laine

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static variables are initialized to zero http://stackoverflow.com/questions/13251083/the-initialization-of-static-variables-in-c – Richard Chambers Mar 01 '15 at 03:13
@RichardChambers yea – Emil Laine Mar 01 '15 at 03:14

Initializing a pointer in C++?

2 Answers2