Re: how to initialize list in a vector

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 27 Sep 2007 09:26:58 -0000

Message-ID:

<1190885218.778348.128890@o80g2000hse.googlegroups.com>

On Sep 26, 3:36 pm, "Andrew Koenig" <a...@acm.org> wrote:

"Baby Lion" <BabyLion.Li...@gmail.com> wrote in message

news:1190792684.579511.266060@d55g2000hsg.googlegroups.com...

list<int> Curve;
vector<Curve> a;
a.reserve(10);
then how should I initialize the list in the vector before
a[0].push_back(123) ?

No need: When you executed

a.reserve(10);

you caused a to have 10 elements, each of which is a vector with no
elements.

Now Andy, you know better than that. He needs a.resize(10) for
that.

Also, of course, his code shouldn't compile, since Curve is a
variable, not a type. He probably needs a typedef in the line
declaring Curve, but I'm not sure. I'm not at all sure what
he's really trying to do, but maybe something like:

    typedef std::list< int > Curve ;
    std::vector< Curve > a( 10 ) ;

is what he's looking for. Or maybe something more like:

    typedef std::list< int > Curve ;
    std::vector< Curve > a ;

    if ( i >= a.size() ) {
        a.resize( i + 1 ) ;
    }
    a[ i ].push_back( 42 ) ;

, if he doesn't know the actual size in advance.

--
James Kanze (GABI Software) email:james.kanze@gmail.com
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