Re: Problem using pointer...

From:

Ian Collins <ian-news@hotmail.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 01 May 2006 14:17:09 +1200

Message-ID:

<4bl9d5F114ag0U1@individual.net>

red floyd wrote:

Ian Collins wrote:

nabeel.girgis@gmail.com wrote:

I am passing a vector by reference into a function and I am trying to
use a pointer in that function.

I get an error saying : '=' : cannot convert from 'std::vector<_Ty> *'
to 'int *'

when I try to initialize the pointer to point to the vector. This is
my first time using pass by reference into a function while trying to
declare a pointer in the same function. My code is given below.

void v_abs(vector<int>&x)
{
int *y;

**** y = &x;

The address of x (&x) is a pointer to vector, not a pointer to int.

Use an iterator instead:

for( std::vector<int>::iterator y = x.begin(); y != x.end(); ++y )
{
  if (*y < 0)
  {
    *y *= -1;
  }
}

I believe the canonical method for turning a vector into a pointer
(usually for passing to a legacy API) is

std::vector<T> v;
// fill v

T* pT = &v[0];

I believe that as of TC1 (C++03), the vector's storage is guaranteed to
be contiguous.

True, but if you are going to iterate over the vector, iterators are the
way to go.

--
Ian Collins.