CODEWITHSUNDEEP
c++linked-list
user2766918
user2766918

Reputation: 584

C++ equivalent of tailq

I'm wondering if there's a standard C++ class which is the equivalent of a tailq. I could use the c implementation of a tailq, but it uses lots of macros and is somewhat ugly.

Basically, I have a class, which each instance has to be part of multiple lists. To avoid extra malloc's/memory dereferences, I'd like to store the next and prev pointers within the class itself. Does C++ have a clever way of doing this, or am I better off just using <sys/queue.h>?

Upvotes: 1

Views: 396

Answers (2)

Eyal K.
Eyal K.

Reputation: 1072

There's no problem storing pointers of the class inside itself. The following code compiles just fine:

class A
{
    A* next;
    A* prev;
};

This will allow you to have pointers for multiple lists inside the object:

class A
{
    std::vector<A*> next;
    std::vector<A*> prev;
};

Upvotes: 0

bolov
bolov

Reputation: 75853

In C++ I would have containers of shared_ptr. It doesn't matter, it can be std::list or std::vector or any container. Because with shared_ptr you have each element allocated separately, I don't see any good reason to use std::list so I would go for std::vector<std::shared_ptr<X>>

Example:

#include <memory>
#include <vector>
#include <iostream>

struct X { int a = 0; X() = default; X(int p) { a = p; } };

auto operator<<(std::ostream& os, X x) -> std::ostream&
{
    os << x.a;
    return os;
}

int main()
{
    auto x1 = std::make_shared<X>(24);
    auto x2 = std::make_shared<X>(11);
    auto x3 = std::make_shared<X>(1024);
    auto x4 = std::make_shared<X>(5);

    std::vector<std::shared_ptr<X>> v1 = {x1, x2, x3, x4};
    std::vector<std::shared_ptr<X>> v2 = {x3, x1, x4};    

    // modify an object and observe the change in both lists
    x1->a = -24;

    for (const auto& e : v1)
        std::cout << *e << ' ';
    std::cout << '\n';

    for (const auto& e : v2)
        std::cout << *e << ' ';
    std::cout << '\n';
}

the output is:

-24 11 1024 5
1024 -24 5

Upvotes: 1

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