Iterator library

Iterator concepts, traits, adaptors, range-access utilities, and the boundary between classic iterators and ranges.

The iterator library is the bridge between algorithms and data structures: it defines how code traverses, reads, writes, advances through, and adapts sequences. This hub is the curated starting point when the question is about iterator capabilities, categories, utilities, or adaptor types rather than a specific container or ranges view.

This page stays focused on iterators and iterator-shaped utilities. It links outward to Ranges, Containers, and Algorithms where the navigation problem becomes broader than iterator mechanics.

# Start Here

Iterator concepts and traversal strength

Start here when you need to know what an iterator is allowed to do: single-pass input, multi-pass forward, bidirectional movement, random access, or contiguous storage guarantees.

input_iterator · forward_iterator · contiguous_iterator

Traits and associated types

Use the traits route when generic code needs `value_type`, `difference_type`, tags, or pointer-like adaptation across iterator types.

iterator_traits · iterator tags · incrementable_traits

Iterator adaptors

Start here when you need to wrap an existing iterator to reverse, move, insert, count, or normalize sentinel/iterator pairs.

reverse_iterator · move_iterator · insert_iterator

Navigation helpers

Use these utilities when you already have iterators and need to move them, measure distance, or obtain begin/end/data/size-style access uniformly.

advance · distance · begin/end

# Quick Map

If you need to...	Start with	Why
Describe how far an iterator can move and what guarantees it has	concepts, iterator tags	This is the route for capability modeling: readable vs writable, single-pass vs multi-pass, random access vs contiguous layout.
Write generic code against iterator-associated types	iterator_traits, incrementable_traits	Traits provide the canonical metadata and defaults that algorithms and generic adapters rely on.
Reverse or move through an existing iterator interface	reverse_iterator, move_iterator	These adaptors change traversal or value category behavior without requiring a different underlying container.
Insert through an iterator facade into a container	insert_iterator, back_insert_iterator, front_insert_iterator	Insertion adaptors are the canonical output-iterator route for algorithms that write into containers.
Advance iterators, compute distances, or get neighboring positions	advance, distance, next, prev	These helpers abstract over traversal strength while preserving the iterator model.
Access a range through non-member `begin`/`end`/`data`/`size` utilities	begin, end, data, size, empty	These are the classic range-access endpoints that bridge arrays, containers, and some view-like types.
Use iterators backed by streams rather than containers	istream_iterator, ostream_iterator, istreambuf_iterator	Stream iterators connect iterator-oriented algorithms to formatted or buffer-level I/O.
Navigate the modern ranges-based iterator/sentinel world	ranges iterator utilities, Ranges hub	Ranges reuse iterator ideas but add sentinels, CPOs, and view-oriented navigation beyond the classic iterator page split.

# Iterator Strength Ladder

Concept	Main guarantee	Use it for
input_iterator	Readable, single-pass traversal	Basic read pipelines, streaming inputs, and sentinel-based one-pass algorithms.
output_iterator	Writable output progression	Algorithm sinks and iterator-based output destinations.
forward_iterator	Multi-pass readable traversal	Stable traversal where revisiting positions is meaningful.
bidirectional_iterator	Can move backward as well as forward	Reverse traversal and predecessor-based algorithms.
random_access_iterator	Constant-time jumps and distance	Index-like traversal, arithmetic on iterators, and random-access algorithms.
contiguous_iterator	Elements occupy contiguous memory	APIs that need raw pointers or contiguous storage guarantees.

# Iterator Families

Traits and tags

Type metadata, iterator categories, difference types, and machinery that generic algorithms inspect.

iterator_traits · iterator tags · incrementable_traits

Traversal adaptors

Adaptors that change how an underlying iterator is traversed or interpreted.

reverse_iterator · move_iterator · counted_iterator · common_iterator

Insertion adaptors

Output-iterator facades that write into containers via insert, push_back, or push_front semantics.

insert_iterator · back_insert_iterator · front_insert_iterator

Stream iterators

Iterator-shaped interfaces for stream extraction/insertion and stream-buffer-level traversal.

istream_iterator · ostream_iterator · istreambuf_iterator · ostreambuf_iterator

Range access helpers

Non-member utility functions that discover iteration endpoints, storage pointers, or size/emptiness information.

begin · end · data · size

Ranges iterator utilities

The CPO-based, sentinel-friendly iterator utilities that live on the boundary between classic iterators and the ranges library.

ranges utilities · Ranges hub

# Utility Operations

Operation	Use it for	Primary destinations
Advance / next / prev	Moving iterators without manually spelling out repeated increment/decrement logic.	advance, next, prev
Distance	Measuring how far apart two positions are according to iterator strength.	distance, ranges::distance
Begin/end/data/size/empty	Uniform access to endpoints and shape information for arrays, containers, and some range-like types.	begin, end, data, size, empty
Iterator-sentinel normalization	Bridging differing iterator/sentinel forms into algorithm-friendly shapes.	common_iterator, default_sentinel_t, unreachable_sentinel_t

# Boundary Lines

This hub covers	Use a different hub for
Iterator concepts, traits, adaptors, stream iterators, and endpoint/navigation utilities.	Ranges for view pipelines and CPO-heavy range navigation, Containers for choosing data structures, and Algorithms for task-oriented operation selection.
Classic iterator-based traversal surfaces.	Ranges when the code is primarily range/view/sentinel-first instead of iterator-pair-first.