C++: What is the difference between std::list and std::forward_list?

list — doubly linked. forward_list — singly linked.

std::list:

• Doubly linked.
• Bidirectional iteration.
• push_front/push_back O(1).
• More memory per node.

1std::list<int> l = {1, 2, 3};
2l.push_front(0);
3l.push_back(4);
4l.reverse();  // Can reverse

std::forward_list:

• Singly linked.
• Forward iteration only.
• push_front O(1).
• Less memory per node.

1std::forward_list<int> fl = {1, 2, 3};
2fl.push_front(0);
3// fl.push_back(4);  // Error!
4// fl.reverse();  // Error!

When to use:

• list — need bidirectional.
• forward_list — memory-constrained.