Is Iteration Order Guaranteed in `std::map`?

Guaranteed Order of Iteration in std::map

The order in which iterators traverse a std::map is guaranteed by the standard. Since std::map is an ordered associative container, elements are organized based on the keys' comparison function.

In the provided example, where the keys are integers, the standard specifies that iterating from std::map::begin() to std::map::end() will ensure that you traverse the elements in ascending order of the keys. This means the example code you provided will indeed print 234, as the keys are stored in sorted order.

It's important to note that the ordering of iterators is a fundamental aspect of std::map's implementation. The ordering is utilized to determine:

• Key Equality: Keys a and b are considered equal if !compare(a,b) && !compare(b,a) is true.
• Efficient Lookup: The ordering enables efficient binary search, making lookups logarithmic in the number of elements.

This guaranteed order provides a predictable and consistent iteration experience, allowing you to rely on the specific order of iterated elements. This can be valuable when performing operations that depend on the key order, such as comparing consecutive elements or extracting specific subsets from the map.

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