---
id: php-constants
title: "PHP Constants"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["define()", "const keyword", "PHP 상수"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.9
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["php", "programming", "w3schools", "constants"]
raw_sources: ["https://www.w3schools.com/php/php_constants.asp"]
applied_in: []
github_commit: ""
---

# [[PHP Constants]]

## 🎯 한 줄 통찰 (One-line insight)
`define()` and `const` aren't interchangeable despite both creating constants — `define()` runs at RUNTIME (so it can live inside functions/conditionals, but never inside a class to define class constants), while `const` runs at COMPILE-TIME (so it must be top-level, but CAN define class constants), making the choice depend entirely on where in the code you need the constant. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Constant** — like a variable but immutable once defined; no `$` sign in the name. [S1]
- **`define(NAME, value)`** — runtime constant creation; always global scope; usable inside functions/conditionals/loops; CANNOT define class constants. [S1]
- **`const NAME = value;`** — compile-time constant creation; must be top-level (not inside functions/loops/if-else/try-catch); CAN define class constants; case-sensitive. [S1]
- **Array constants** — both `define()` and `const` support array values. [S1]

## 📖 세부 내용 (Details)
- define() basic: `define("GREETING", "Welcome to W3Schools.com!"); echo GREETING;`. [S1]
- define() inside a function still creates a global constant: `function myTest() { define("GREETING", "Welcome to W3Schools.com!"); } myTest(); echo GREETING; // accessible outside`. [S1]
- const basic: `const GREETING = "Welcome to W3Schools.com!"; echo GREETING;`. [S1]
- Array constants: `define("CARS", array("Volvo", "BMW", "Toyota")); echo CARS[0]; const ANIMALS = array("Cat", "Dog", "Horse"); echo ANIMALS[1];`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **define()과 const의 근본적 차이**: define()은 런타임에 실행되어 함수/조건문 내부에 선언 가능하지만 클래스 상수 정의 불가, const는 컴파일타임에 처리되어 최상위 스코프에서만 선언 가능하지만 클래스 상수 정의는 가능하다는 점이 명확히 대비됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 함수 내부에서 define()으로 전역 상수를 선언하고 함수 밖에서 접근하는 패턴이 define()의 특이한 스코프 동작을 보여준다. [S1]

## 💻 코드 패턴 (Code patterns)
define() creates a global constant even when called inside a function (PHP):
```php
function myTest() {
    define("GREETING", "Welcome to W3Schools.com!");
}
myTest();
echo GREETING; // accessible here, outside the function
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.90
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[PHP Tutorial]]
- **관련 개념:** [[PHP Magic Constants]], [[PHP OOP Constants]], [[PHP Variables]]
- **참조 맥락:** 상수 정의 두 가지 방법 — 매직 상수(Magic Constants) 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — PHP Constants — https://www.w3schools.com/php/php_constants.asp

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