[output.iterators]

24 Iterators library [iterators]

24.3 Iterator requirements [iterator.requirements]

24.3.5 C++17 iterator requirements [iterator.cpp17]

24.3.5.4 Output iterators [output.iterators]

A class or pointer type X meets the requirements of an output iterator if X meets the Cpp17Iterator requirements ([iterator.iterators]) and the expressions in Table 80 are valid and have the indicated semantics.

Table 80 — Cpp17OutputIterator requirements (in addition to Cpp17Iterator) [tab:outputiterator]

🔗 Expression	Return type	Operational	Assertion/note
🔗		semantics	pre-/post-condition
🔗 *r = o	result is not used		Remarks: After this operation r is not required to be dereferenceable. Postconditions: r is incrementable.
🔗 ++r	X&		addressof(r) == addressof(++r). Remarks: After this operation r is not required to be dereferenceable. Postconditions: r is incrementable.
🔗 r++	convertible to const X&	{ X tmp = r; ++r; return tmp; }	Remarks: After this operation r is not required to be dereferenceable. Postconditions: r is incrementable.
🔗 *r++ = o	result is not used		Remarks: After this operation r is not required to be dereferenceable. Postconditions: r is incrementable.

Recommended practice: The implementation of an algorithm on output iterators should never attempt to pass through the same iterator twice; such an algorithm should be a single-pass algorithm.

[Note 1:

The only valid use of an operator* is on the left side of the assignment statement.

Assignment through the same value of the iterator happens only once.

Equality and inequality are not necessarily defined.

— end note]