[Tyagiquamar]

Summary of Changes

Fixes #865

In standard C++ containers with equivalent keys (std::multimap and std::multiset), the relative order of elements that compare equivalent is required to be preserved as their order of insertion.

Previously, pair_associative_container.hpp and set.hpp initialized their insertion hint to map.begin() / set.begin(), and then passed the iterator returned by emplace_hint() into the next iteration. Because associative container hint insertion inserts the new element immediately prior to the hint position, using the previous element's iterator as a hint caused each successive equivalent key to be inserted before the preceding one, reversing the order of equivalent keys on every serialization round-trip.

This change fixes the deserialization behavior:

• Updated pair_associative_container.hpp to pass map.end() as the insertion hint. Because serialized archives are written in forward sorted order, incoming elements belong at the end of the container, preserving the original sequence of equivalent keys in O(1) amortized insertion time.
• Updated set.hpp to pass set.end() as the insertion hint for set and multiset containers.
• Enhanced unittests/multimap.hpp and unittests/multiset.hpp with full sequence equality assertions (std::equal) in addition to count checks.
• Added deterministic duplicate-key ordering tests across Binary, Portable Binary, XML, and JSON archives in unittests/multimap.cpp and unittests/multiset.cpp.

---

Verification

All unit tests passed in Linux Docker (gcc:14.3.0):

[doctest] test cases: 4 | 4 passed | 0 failed
[doctest] assertions: 804008 | 804008 passed | 0 failed
[doctest] test cases: 4 | 4 passed | 0 failed
[doctest] assertions: 404008 | 404008 passed | 0 failed
100% tests passed, 0 tests failed out of 8

[redchairman]

您的邮件我已收到，谢谢合作！