CODEWITHSUNDEEP
c++
Chester Heng
Chester Heng

Reputation: 27

Insert objects into a list

Any kind soul know how to correct the following code

"d1.insert(d1.begin(), it[0]);" so the the output is as follow:

program will run successfuly and display: 1 2 3 4 5 6 7 8 9 10

#include <list>
#include <deque>
#include <iostream>

using namespace std;

template<typename T> ostream & print(const T & start, const T & end)
{
    T tmp = start;
    for(; tmp != end; ++tmp)
    {
            cout<< *tmp<< " ";
    }
    return cout;
}
class A
{
public:
    int a;
public:
    A(int a):a(a) {}
    A(const A & a) {}
};

ostream & operator<<(ostream & c, const A & o)
{
    c<<o.a;
    return c;
}

int main()
{
    int tab[]={1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    list<A> l1(tab, tab+10);
    deque<A> d1;
    list<A>::iterator it;
    for(it = l1.begin(); it != l1.end(); ++it)
    {
            d1.insert(d1.begin(), it[0]);
    }
    print(d1.begin(), d1.end())<<endl;
    return 0;
}

Upvotes: 1

Views: 506

Answers (2)

PaulMcKenzie
PaulMcKenzie

Reputation: 35440

An alternative is just to use std::copy:

#include <algorithm>
#include <iterator>
//...
std::copy(l1.begin(), l1.end(), std::back_inserter(d1));

There are other issues with your code you should correct:

1) Remove the empty A copy constructor. By making it empty, you're creating A copies that will not copy the a member.

2) The parameter to the A constructor should be different than the name of the member variable.

See the Live Example

Upvotes: 1

sjrowlinson
sjrowlinson

Reputation: 3355

It seems from the code that you want to insert to a std::deque not a std::list (you already inserted the array values into the list l1). You could follow the same procedure to insert to the std::deque:

int main(void) {
    int tab[] = { 1,2,3,4,5,6,7,8,9,10 };
    std::list<int> l1(tab, tab + 10);
    std::deque<int> d1(tab, tab + 10);
}

where I have simply replaced A by int here as the former looks just to be a wrapper for an int.

Alternatively you could do,

int main(void) {
    int tab[] = { 1,2,3,4,5,6,7,8,9,10 };
    std::list<int> l1(tab, tab + 10);
    std::deque<int> d1;

    auto it = d1.begin();
    d1.insert(it, l1.begin(), l1.end());
}

Upvotes: 2

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