Vector of vector question

[BCC]

If I create a vector of vectors of double:

std::vector< std::vector<dou ble> > table1;

Are my vectors of doubles uninitialized? Do I have to loop through table1
and initialize each vector of doubles using new?

And in cleaning up, manually delete each of these vectors of doubles?

Thanks,
B

[Daniel T.]

de*********@hot mail.com (Gavin Deane) wrote:

"David Fisher" <no****@nospam. nospam.nospam> wrote in message

"Daniel T." <po********@eat hlink.net> wrote:

Are you sure you want to use a vector of vectors? I would only do that
if I needed a ragged array. If the array represents a table, you would
be better off creating a 2D array class. See the FAQ for a sample
implementation.

The reference is
http://www.parashift.com/c++-faq-lit...html#faq-16.17 if you
didn't already have it.

David F

The next FAQ shows the same thing using a vector of vectors to
implement the 2D array class.

http://www.parashift.com/c++-faq-lit...html#faq-16.18

Removes all the need for explicit memory management in the class. And
it should be easy to design the class so that it's impossible for the
individual vectors-within-a-vector to end up with different sizes.

A better choice, of course would be to implement the 2D array using a
single vector. This also removes the need for explicit memory management
and is easer to design...

[RanggaPratama]

Now, how do we initialize the 2d vector?

I tried to intialize the 2d vector by doing:(but, it's not working)

for(int i = 0; i < row; i++)
for(int j = 0; j < col; j++)
table1[i].push_back(1);

I knew it wouldn't work. I was just trying to do different things.

I was thinking of using iterator, but I don't have any idea how to do it with 2d vector.

[Clark Cox]

In article
<17************ *************** ***@localhost.t alkaboutprogram ming.com>,
"RanggaPrat ama" <ma*******@hotm ail.com> wrote:

Now, how do we initialize the 2d vector?

I tried to intialize the 2d vector by doing:(but, it's not working)

for(int i = 0; i < row; i++)
for(int j = 0; j < col; j++)
table1[i].push_back(1);

I knew it wouldn't work. I was just trying to do different things.
You're not doing anything to change the size of the outer vector.
Since you said "initialize , I assume that the vector is empty to begin
with, so table1[i] is undefined.
I was thinking of using iterator, but I don't have any idea how to do it with
2d vector.

How about (where T is whatever type the inner vector contains):

{
table1.clear();
table1.resize(r ow, std::vector<T>( col, 1));
}