2nd/10_Wiki/Topics/Domain_Programming/Topic_PHP/PHP_Constants.md

id, title, category, status, verification_status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, created_at, updated_at, review_reason, merge_history, tags, raw_sources, applied_in, github_commit

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

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):

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).