---
id: cpp-iterators
title: "C++ Iterators"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["begin() end()", "vector iterator", "C++ 반복자"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.86
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["cpp", "programming-language", "w3schools", "stl", "iterator"]
raw_sources: ["https://www.w3schools.com/cpp/cpp_iterators.asp"]
applied_in: []
github_commit: ""
---

# [[CPP Iterators]]

## 🎯 한 줄 통찰 (One-line insight)
An iterator is a pointer with a container-agnostic interface — `*it` dereferences and `++it` advances exactly like a raw C pointer walking an array, but the SAME `begin()`/`end()`/`*it`/`++it` syntax works identically across vector, list, deque, set, AND map, which is precisely the capability C's raw pointers never had (a `int*` walking an array shares no interface with a linked-list traversal via `node->next`) — and this uniform interface is *why* for-each loops and generic algorithms like `sort()`/`find()` can operate on any container without being rewritten per container type. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Iterator = a "pointer" to an element** — used to access/iterate through data structures by pointing to elements rather than copying them. [S1]
- **`begin()` / `end()`** — functions belonging to the CONTAINER (not the iterator) that return an iterator to the first element / to one-past-the-last element; `end()` never points to a real element, only marks the stopping condition. [S1]
- **`*it`** — dereference operator, accesses the value the iterator currently points to (and can assign through it: `*it = "Tesla";` modifies the container in place). [S1]
- **`++it`** — advances the iterator to the next element. [S1]
- **`auto` keyword** — lets the compiler infer the verbose iterator type (`vector<string>::iterator`) automatically; works in the loop declaration itself. [S1]
- **For-each vs. iterator** — for-each is simpler for read-only traversal; iterators are required when you need to modify, erase, iterate in reverse, or skip elements during the loop. [S1]
- **`.erase(it)` inside a loop** — removing an element mid-iteration returns the NEXT valid iterator, which is why the erase-loop pattern reassigns `it = cars.erase(it);` instead of also calling `++it`. [S1]
- **`rbegin()` / `rend()`** — reverse-order counterparts to `begin()`/`end()`, for iterating backward. [S1]
- **Iterator support is not universal** — vector, list, deque, map, and set support iterators; stack and queue do NOT. [S1]
- **Iterators power `<algorithm>` functions** — `sort()`, `find()`, etc. take a begin/end iterator pair as parameters rather than the container itself. [S1]

## 📖 세부 내용 (Details)
- Basic loop: `vector<string>::iterator it; for (it = cars.begin(); it != cars.end(); ++it) { cout << *it; }`. [S1]
- `auto` shorthand: `for (auto it = cars.begin(); it != cars.end(); ++it) { cout << *it; }`. [S1]
- Erase-during-iteration pattern: `for (auto it = cars.begin(); it != cars.end(); ) { if (*it == "BMW") { it = cars.erase(it); } else { ++it; } }` — no `++it` in the header since erase already advances. [S1]
- Reverse iteration: `for (auto it = cars.rbegin(); it != cars.rend(); ++it) { cout << *it; }`. [S1]
- Map iteration needs `->first`/`->second` (arrow, since `it` is a pointer-like object to a pair): `for (auto it = people.begin(); it != people.end(); ++it) { cout << it->first << it->second; }`. [S1]
- `sort(cars.begin(), cars.end());` from `<algorithm>` — the same begin/end pair used for manual loops is reused as the algorithm's range argument. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **C의 원시 포인터에는 없던 통일 인터페이스가 도입됨**: C에서 배열은 포인터 산술(`arr + i`)로, 연결 리스트는 `node->next`로 순회 방식이 완전히 달랐지만, C++ iterator는 vector/list/deque/set/map 모두에서 동일한 `begin()`/`end()`/`*it`/`++it` 문법을 재사용한다는 점이 핵심 차이로 확인됨. [S1]
- **stack/queue는 iterator를 지원하지 않음**: vector/list/deque/map/set과 달리, 접근 지점이 의도적으로 제한된 stack과 queue는 iterator 자체를 지원하지 않는다는 점이 명시적으로 확인됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
vector에서 특정 값("BMW")을 가진 요소를 순회 중에 삭제하는 예제가 iterator가 for-each보다 유리한 실전 사례로 원문에서 제시됨. [S1]

## 💻 코드 패턴 (Code patterns)
Iterator-based erase during traversal — impossible with a simple for-each (C++):
```cpp
#include <vector>
vector<string> cars = {"Volvo", "BMW", "Ford", "Mazda"};

for (auto it = cars.begin(); it != cars.end(); ) {
  if (*it == "BMW") {
    it = cars.erase(it);  // erase returns the next valid iterator
  } else {
    ++it;
  }
}
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.86
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[C++ Tutorial]]
- **관련 개념:** [[CPP Maps]], [[CPP Algorithms]], [[CPP Pointers]], [[CPP Auto]]
- **참조 맥락:** 데이터 구조(STL) 섹션 — Algorithms 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — C++ Iterators — https://www.w3schools.com/cpp/cpp_iterators.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "C++ Iterators" page (Astra wiki-curation, P-Reinforce v3.1 format).
