2nd/10_Wiki/Dev/Topic_PHP/PHP_String_Slicing.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-string-slicing	PHP String Slicing	Programming_Language	draft	conceptual		substr() PHP 문자열 슬라이싱		B	0.9	2026-07-04	2026-07-04			php programming w3schools strings substr	https://www.w3schools.com/php/php_string_slicing.asp

PHP String Slicing

🎯 한 줄 통찰 (One-line insight)

substr()'s length parameter can itself be NEGATIVE — meaning "stop N characters before the end" rather than "take N characters" — so substr($x, 5, -3) reads as "start at index 5, and go until you're 3 characters from the end," a dual meaning of the third parameter that requires care since negative start and negative length behave completely differently. [S1]

🧠 핵심 개념 (Core concepts)

• substr(string, start, length) — extracts a substring. [S1]
• Positive start — 0-indexed position to begin the slice. [S1]
• Omitted length — slices to the end of the string. [S1]
• Negative start — counts from the end (-1 is the last character). [S1]
• Negative length — stops that many characters BEFORE the end, rather than taking that many characters. [S1]

📖 세부 내용 (Details)

• Basic slice: $x = "Hello World!"; echo substr($x, 6, 5); // "World". [S1]
• To the end (no length): echo substr($x, 6); // "World!". [S1]
• Negative start: echo substr($x, -5, 3); // "Wor" (starting from index -5). [S1]
• Negative length: $x = "Hi, how are you?"; echo substr($x, 5, -3); // "ow are y" (stop 3 chars before the end). [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• 음수 길이의 의미: 길이 파라미터가 음수일 경우 "가져올 문자 수"가 아니라 "끝에서부터 생략할 문자 수"로 해석된다는 점이 예제로 명확히 검증됨. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — 문장 끝 몇 글자를 제외한 나머지를 추출하는 것이 음수 길이 파라미터 활용의 대표 사례다. [S1]

💻 코드 패턴 (Code patterns)

Negative length stops before the end of the string (PHP):

$x = "Hi, how are you?";
echo substr($x, 5, -3); // "ow are y"

✅ 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 String Concatenate, PHP String Escape, PHP Numbers
• 참조 맥락: 문자열 일부 추출 — 이스케이프 문자(Escape) 챕터로 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — PHP - Slicing Strings — https://www.w3schools.com/php/php_string_slicing.asp

📝 변경 이력 (Change history)

• 2026-07-04: Initial draft synthesized from the W3Schools "PHP - Slicing Strings" page (Astra wiki-curation, P-Reinforce v3.1 format).