Re: Vector reserve in a for_each

From:

Alan Johnson <awjcs@yahoo.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 24 Feb 2007 00:42:57 -0800

Message-ID:

<LI2dnf1QnqcMZ0LYnZ2dnUVZ_ovinZ2d@comcast.com>

Chris Roth wrote:

I have a vector of vectors:
    vector< vector<double> > v;
and have initialized it with:
    v( 5 );
as I know I will have 5 columns of data. At this point, I read text file
data into each of the the vectors using push_back. I know that I will be
reading in 5000 elements into each vector, so I use reserve:
    ifstream f( "file.txt" );
    if(f.is_open())
    {
        for( vector< vector<double> >::iterator itr = v.begin();
             itr != v.end(); ++itr )
        {
            itr->reserve(5000);
        }
        double d;
        while(f >> d)
        {
            m_data[0].push_back( d );
            f >> d;
            m_data[1].push_back( d );
            f >> d;
            m_data[2].push_back( d );
            f >> d;
            m_data[3].push_back( d );
            f >> d;
            m_data[4].push_back( d );
        }
    }
However, could I use a for_each to set the reserve of the vectors? Or is
there a different/better way to read in the 5 column text data?

Thanks in advance.

Here's how you'd do it. But I would comment that in the amount of time
it took me to get the syntax just right I could have written the
equivalent for loop a hundred times over.

#include <vector>
#include <functional>
#include <algorithm>

int main()
{
     std::vector< std::vector<double> > v(5) ;

     std::for_each(v.begin(), v.end(),
         std::bind2nd(std::mem_fun_ref(&std::vector<double>::reserve),
5000)) ;
}

--
Alan Johnson