Re: vector question

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Mon, 19 Jun 2006 12:34:29 -0400

Message-ID:

<e76jmo$lgd$1@news.datemas.de>

Babis Haldas wrote:

Can you please tell me whats wrong with the follow code
Its crasing in the line
cout << v[0]->x1 << endl;
when accesing the first element of the vector
If i define the vector as
vector<foo*>v ;
everything is ok

why it doesnt like v(10) ?

Because if you don't specify the size, it creates an *empty* vector,
in which you later insert the *real* (non-null) element, which you
later access.

thanks

#include <iostream>
#include <vector>

using namespace std;

struct foo {
       int x1;
       int x2;
};

int main()
{
       vector<foo*> v(10);

That creates a ten-sized vector of pointers to 'foo', each null (IIRC).

       foo * p;
       p = new foo;
       p->x1 = 111;
       p->x2 = 222;
       v.push_back(p);

That inserts *yet another* pointer to 'foo' at the end of the vector.

cout << v[0]->x1 << endl;

v[0] is a null pointer. You try dereferencing it. Undefined behaviour.

}

V
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