Can You Modify Elements Directly in an std::set?

Modifying Elements in an std::set: Undefined Behavior

Question:

When modifying an element of an std::set, such as through an iterator, what happens? Is it undefined behavior?

Answer:

Modifying the value of an element directly in an std::set is not allowed and triggers undefined behavior. This is stated in the MSDN documentation, which states:

"The value of an element in a set may not be changed directly. Instead, you must delete old values and insert elements with new values."

The reason for this is that the set implementation, typically a red-black tree, relies on the uniqueness and ordering of the values. Modifying an element's value directly without informing the set can result in incorrect tree ordering and unpredictable behavior, such as erroneous search results.

Therefore, it is essential to follow proper set usage and modify elements by removing and inserting new values with the correct key instead of directly changing existing ones.

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