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

forward_list — singly linked. list — doubly linked.

std::forward_list (C++11):

• Singly linked list.
• Less memory (no back pointer).
• Forward iteration only.
• O(1) insert/delete.

1std::forward_list<int> fl = {1, 2, 3};
2fl.push_front(0);  // O(1)
3// fl.back();  // Error! No back()

std::list:

• Doubly linked list.
• More memory.
• Bidirectional iteration.
• O(1) insert/delete.

1std::list<int> l = {1, 2, 3};
2l.push_back(4);  // O(1)
3l.back();  // OK

When to use:

• forward_list — memory-constrained, forward-only.
• list — need bidirectional traversal.