C++: What is the difference between std::move and std::forward?

std::move — cast to rvalue. std::forward — perfect forwarding.

std::move:

• Unconditionally casts to rvalue.
• Used for moving objects.

1std::string s1 = "hello";
2std::string s2 = std::move(s1);  // s1 is now empty
3
4// After move, s1 is in valid but unspecified state

std::forward:

• Conditionally casts based on template parameter.
• Used for perfect forwarding.

1template<typename T>
2void wrapper(T&& arg) {
3    // If arg was lvalue, forward as lvalue
4    // If arg was rvalue, forward as rvalue
5    func(std::forward<T>(arg));
6}

Key differences:

• std::move — always rvalue.
• std::forward — preserves original category.
• std::move — for moving.
• std::forward — for forwarding.