Is the Iteration Order of Elements in a std::map Guaranteed?

Guaranteed Ordering of std::map Iterations

In a std::map, elements are sorted according to their keys, ensuring an ascending order of key values. This characteristic raises the question of whether the iteration order of elements through std::map iterators is also guaranteed in terms of key values.

Answer:

Yes, the iteration order is guaranteed by the C standard. When iterating from std::map::begin() to std::map::end(), elements will be traversed in ascending order of key values.

Example:

Consider the following code snippet:

<code class="cpp">std::map<int, int> map_;
map_[1] = 2;
map_[2] = 3;
map_[3] = 4;
for( std::map<int, int>::iterator iter = map_.begin();
     iter != map_.end();
     ++iter )
{
    std::cout << iter->second;
}</code>

This code will guaranteedly print 234, as the iteration order is guaranteed to follow the sorted keys 1, 2, 3.

Implications:

This ordering is not a mere coincidence but a fundamental aspect of std::map. It is utilized for determining when two key values are considered equal and for efficient logarithmic-complexity binary searches.

Conclusion:

The iteration order of std::map ensures consistent and reliable access to elements in ascending order of key values. This guarantees efficient and predictable operation.

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