Re: About for_each usage

From:

fgh.vbn.rty@gmail.com

Newsgroups:

comp.lang.c++

Date:

Wed, 2 Jul 2008 17:23:45 -0700 (PDT)

Message-ID:

<27bc8c0a-2070-445f-9a08-b514dc305263@c58g2000hsc.googlegroups.com>

Ivan Novick wrote:

On Jul 2, 3:27=EF=BF=BDpm, fgh.vbn....@gmail.com wrote:

I'm having problems setting up the functors to use for_each. Here's an
example:

class A {
public:
=EF=BF=BD =EF=BF=BD void getName() { return name; }
private:
=EF=BF=BD =EF=BF=BD string name;

};

class B {
public:
=EF=BF=BD =EF=BF=BD =EF=BF=BDvector<int> getIds { return vi; }
=EF=BF=BD =EF=BF=BD =EF=BF=BDA& getA(int idx) { return vA.at(idx); }
=EF=BF=BD =EF=BF=BD =EF=BF=BDvoid bfunc();
private:
=EF=BF=BD =EF=BF=BD =EF=BF=BDvector<A> vA;
=EF=BF=BD =EF=BF=BD =EF=BF=BDvector<int> vi;

}

class C {
public:
=EF=BF=BD =EF=BF=BD =EF=BF=BDvoid cfunc();
private:
=EF=BF=BD =EF=BF=BD =EF=BF=BDB b;

}

void B::bfunc()
{
=EF=BF=BD =EF=BF=BD// populate vi
=EF=BF=BD =EF=BF=BDfor(int i=0; i<vi.size(); ++i) {
=EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD cout << vA[i].printName() << en=

dl;

=EF=BF=BD =EF=BF=BD}

}

void C::cfunc()
{
=EF=BF=BD =EF=BF=BD// populate vi
=EF=BF=BD =EF=BF=BDvector<int> vc = b.getIds();
=EF=BF=BD =EF=BF=BDfor(int i=0; i<vc.size(); ++i) {
=EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD A& a = getA(vc[i]);
=EF=BF=BD =EF=BF=BD =EF=BF=BD =EF=BF=BD cout << a.getName() << endl;
=EF=BF=BD =EF=BF=BD}

}

Here vA is just a vector of As and vi is a vector of integers that
index into vA. Let's suppose that vA and vi are populated
appropriately. All I'm trying to do is to execute a particular
function on a subset of the As.

I have three questions:
1) How do I replace the for loop in bfunc with a for_each?
2) How do I replace the for loop in cfunc with a for_each?
3) How would I do this using the Boost.Lambda functions?

Thanks.

Hi,

Your code has too many syntax errors as is to give advice on how to
modify it. Can you first make it compile and then repost it.

Ivan Novick
http://www.mycppquiz.com

Sorry, I should've tried it out first. Anyway, the following compiles
without errors on gcc v3.0.4.

#include <iostream>
#include <string>
#include <vector>

using namespace std;

class A {
public:
    std::string getName() { return name; }
private:
    std::string name;
};

class B {
public:
    vector<int> getIds() { return vi; }
    A& getA(int idx) { return vA.at(idx); }
    void bfunc();
private:
    vector<A> vA;
    vector<int> vi;

};

class C {
public:
    void cfunc();
private:
    B b;
};

void B::bfunc()
{
    // populate vA and vi in some fashion
    for(int i=0; i<vi.size(); ++i) {
        std::cout << vA[i].getName() << std::endl;
    }
}

void C::cfunc()
{
    // populate vA and vi in some fashion
    vector<int> vc = b.getIds();
    for(int i=0; i<vc.size(); ++i) {
        A& a = b.getA(vc[i]);
        std::cout << a.getName() << std::endl;
    }
}