Re: Is there an STL algo to fill a vector with product of 2 other vectors?

From:

red floyd <no.spam.here@example.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 09 Dec 2008 12:35:33 -0800

Message-ID:

<xEA%k.7959$as4.3709@nlpi069.nbdc.sbc.com>

Steve555 wrote:

On 9 Dec, 17:09, James Kanze <james.ka...@gmail.com> wrote:

On Dec 9, 3:43 pm, Steve555 <foursh...@btinternet.com> wrote:

I'm looking for an algorithm that takes 2 vectors and a
function pointer as arguments? I want to use the function
pointer to calculate a result e.g. the product, and put the
result either in place, or in a third vector.
I've looked through the list of algorithms and there doesn't
appear to be one. transform() is the closest, but alas works
on only a single vector.

There are two versions of std::transform. The following code
should do the trick:
    assert( v1.size() == v2.size() ) ;
    std::transform( v1.begin(), v1.end(),
                    v2.begin(),
                    std::back_inserter( v3 ),
                    std::multiplies< double >() ) ;

--
James Kanze (GABI Software) email:james.ka...@gmail.com
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Thanks James, but I wasn't sure why you used std::back_inserter()?

because that will push_back() the results onto the v3. Otherwise, you
risk running off the end of the resultant, especially if it's empty.