---
id: cpp-queues
title: "C++ Queues"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["std::queue", "FIFO", "C++ 큐"]
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", "queue", "fifo"]
raw_sources: ["https://www.w3schools.com/cpp/cpp_queues.asp"]
applied_in: []
github_commit: ""
---

# [[CPP Queues]]

## 🎯 한 줄 통찰 (One-line insight)
`queue` is stack's mirror image — same restricted-access philosophy (no arbitrary indexing, no brace-list initialization, only `.push()`/`.pop()`), but instead of both ends collapsing onto one "top," a queue keeps `.front()` and `.back()` as two DISTINCT accessible ends, encoding FIFO order (supermarket line: first in line, first served) the same way stack encoded LIFO — the two containers share nearly identical method names (`.push()`, `.pop()`, `.size()`, `.empty()`) but differ in exactly which end `.pop()` removes from, which is the single fact that determines whether a container behaves like a stack or a queue. [S1]

## 🧠 핵심 개념 (Core concepts)
- **FIFO (First In, First Out)** — the first element added is the first one removed, unlike stack's LIFO. [S1]
- **`queue<type> name`** — requires `<queue>`; like stack, CANNOT be initialized with a curly-brace list at declaration — must use `.push()` after declaring. [S1]
- **`.push()`** — adds an element to the BACK (end) of the queue. [S1]
- **`.front()` / `.back()`** — TWO accessible points (unlike stack's single `.top()`): front is the oldest/first element, back is the newest/last element; both are also assignable. [S1]
- **`.pop()`** — removes the FRONT element (the oldest one) — this is the key difference from stack's `.pop()`, which removes from the top/back instead. [S1]
- **`.size()` / `.empty()`** — same semantics as stack/list/vector. [S1]

## 📖 세부 내용 (Details)
- Declaration + fill: `queue<string> cars; cars.push("Volvo"); cars.push("BMW"); cars.push("Ford"); cars.push("Mazda");` — resulting order: Volvo(front), BMW, Ford, Mazda(back). [S1]
- Access/modify: `cars.front()` → "Volvo", `cars.back()` → "Mazda"; both can be reassigned directly (`cars.front() = "Tesla";`). [S1]
- Remove: `cars.pop();` removes Volvo (the front/oldest), making BMW the new front. [S1]
- Same brace-initialization restriction as stack is called out explicitly: `queue<string> cars = {"Volvo", ...};` is not allowed. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **stack과 동일한 메서드명, 반대 방향 의미**: stack의 `.pop()`은 top(가장 최근 추가된 요소)을 제거했지만, queue의 `.pop()`은 front(가장 오래된 요소)를 제거한다는 점이 이번 챕터에서 stack과의 핵심 대비로 확인됨 — 메서드 이름은 같아도 동작 방향이 정반대. [S1]
- **접근 가능 지점이 하나에서 둘로 늘어남**: stack은 `.top()` 하나만 노출했지만, queue는 `.front()`와 `.back()` 두 지점을 모두 노출한다는 점이 FIFO 구조의 특성상 필요한 차이로 확인됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 슈퍼마켓 줄서기에 비유해 FIFO를 설명하고, 자동차 이름을 push()로 채운 뒤 front()/back()으로 확인하는 예제가 원문에서 제시됨. [S1]

## 💻 코드 패턴 (Code patterns)
Queue push/front/back/pop — pop always removes from the front, unlike stack (C++):
```cpp
#include <queue>
queue<string> cars;
cars.push("Volvo");
cars.push("BMW");
cars.push("Ford");
cars.push("Mazda");

cout << cars.front();  // "Volvo" (oldest)
cout << cars.back();   // "Mazda" (newest)
cars.pop();             // removes "Volvo" (the front)
cout << cars.front();  // now "BMW"
```

## ✅ 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 Stacks]], [[CPP Data Structures]], [[CPP Deque]]
- **참조 맥락:** 데이터 구조(STL) 섹션 — Stacks와 짝을 이루는 챕터, 다음은 Deque.

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

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