2nd/10_Wiki/Dev/Topic_C/C_Strings_Functions.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
c-strings-functions	C String Functions	Programming_Language	draft	conceptual		strlen strcat strcpy strcmp string.h C 문자열 함수		B	0.86	2026-07-04	2026-07-04			c programming-language w3schools strings string-functions	https://www.w3schools.com/c/c_strings_functions.php

C String Functions

🎯 한 줄 통찰 (One-line insight)

strlen() and sizeof() measure fundamentally different things and diverge sharply once a buffer is oversized — for a 26-letter alphabet stored in a 50-byte array, strlen() still correctly reports 26 (it counts up to the \0), while sizeof() reports 50 (the array's total allocated memory), meaning sizeof is NEVER a reliable way to get "string length" once the array is larger than the string it holds. [S1]

🧠 핵심 개념 (Core concepts)

• <string.h> — the header required to use C's built-in string functions. [S1]
• strlen(str) — returns the string's character count UP TO (not including) the \0 terminator. [S1]
• sizeof(arr) — returns the array's total allocated memory in bytes, INCLUDING the \0 and any unused trailing space — not the string's actual content length. [S1]
• strcat(dest, src) — appends src onto the end of dest; dest's buffer must be large enough to hold both strings combined. [S1]
• strcpy(dest, src) — copies src's value into dest; dest's buffer must be large enough for the copied content. [S1]
• strcmp(str1, str2) — returns 0 if the strings are equal, a non-zero value otherwise. [S1]

📖 세부 내용 (Details)

• strlen vs sizeof on an exactly-sized array: char alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; strlen(alphabet) // 26, sizeof(alphabet) // 27 (27 includes \0). [S1]
• strlen vs sizeof on an OVERSIZED array — the critical divergence: char alphabet[50] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; strlen(alphabet) // still 26, sizeof(alphabet) // 50 (the array's declared capacity, not content length). [S1]
• Concatenation requiring a big-enough destination buffer: char str1[20] = "Hello "; char str2[] = "World!"; strcat(str1, str2); printf("%s", str1);. [S1]
• Comparison returning 0 for equal strings, non-zero otherwise: strcmp(str1, str2); // 0 if equal / strcmp(str1, str3); // -4 if not equal. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• sizeof는 문자열 길이 측정 도구가 아님: 배열 크기가 실제 문자열보다 클 경우 sizeof는 할당된 전체 메모리(50)를 반환하지만 strlen은 여전히 실제 내용 길이(26)를 정확히 반환한다는 점이 명시적으로 대비됨 — sizeof를 문자열 길이 측정에 쓰면 안 된다는 강력한 경고. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — strcat으로 "Hello "와 "World!"를 합치는 예제가 문자열 연결의 표준 실전 활용이며, 대상 버퍼 크기를 미리 충분히 확보해야 한다는 주의사항이 함께 강조된다. [S1]

💻 코드 패턴 (Code patterns)

strlen() and sizeof() diverging once the buffer is larger than the actual string content (C):

char alphabet[50] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
printf("%zu\n", strlen(alphabet));   // 26 (actual content length)
printf("%zu\n", sizeof(alphabet));   // 50 (total allocated buffer size)

✅ 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: C Strings Esc, C Data Types Sizeof, C Math
• 참조 맥락: 문자열 섹션 마지막 — 수학 함수(Math) 섹션으로 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — C String Functions — https://www.w3schools.com/c/c_strings_functions.php

📝 변경 이력 (Change history)

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