Re: How to copy vector?

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Wed, 27 Jan 2010 01:58:11 +0100

Message-ID:

<hjo334$3be$1@news.eternal-september.org>

* Immortal Nephi:

I create two vector variables. First variable: data is initialized
with integers. Second variable: copyData is empty. Both have same
sizes.

'copyData' contains 100 zeroes.

How do I write correct code to copy all elements from data to
copyData?

Just an assignment (for example), as you do below.

I don?t have to go through iterator loop to copy each
element.
I want to know that vector data should be auto storage in the global
function?s stack frame. Then, the return type will be vector to copy
all elements.
If result size is different and is more than 100 elements, will
copyData be automatically resized?

Yes.

vector< int > foo()
{
    int numData = 1;
    vector< int > result;
    result.resize( 100 );

    for( vector< int >::iterator it = result.begin();
        it != result.end(); ++it )
        *it = numData++;

    return result;
}

You could write this more easily as

   vector<int> foo()
   {
       vector<int> result;
       for( int i = 1; i <= 100; ++i )
       {
           result.push_back( i );
       }
       return result;
   }

int main()
{
vector< int > copyData;
copyData.resize( 100 );

This size specification is not necessary.

copyData = foo();

return 0;

And this 'return' isn't necessary either. 'main' returns 0 by default. :-)

}

Cheers & hth.,

- Alf