2nd/10_Wiki/Topic_Programming/Topic_C/C_Errors.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-errors	C Errors	Programming_Language	draft	conceptual		compile-time vs runtime errors use-after-free C 에러		B	0.86	2026-07-04	2026-07-04			c programming-language w3schools errors	https://www.w3schools.com/c/c_errors.php

C Errors

🎯 한 줄 통찰 (One-line insight)

The three runtime error examples (divide-by-zero, out-of-bounds array access, use-after-free) all share a common trait the source doesn't state explicitly but demonstrates through selection: NONE of them are caught by the compiler — all three compile cleanly and only misbehave when actually EXECUTED — meaning C's compile-time checking is fundamentally limited to syntax/type issues, while logic and memory-safety issues are entirely the programmer's responsibility to prevent at runtime. [S1]

🧠 핵심 개념 (Core concepts)

• Compile-time errors — prevent the program from compiling at all; e.g. missing semicolon, undeclared variable, mismatched types (assigning a string literal to an int). [S1]
• Runtime errors — the program compiles successfully but crashes or misbehaves when RUN; e.g. division by zero, out-of-bounds array access, using memory after free(). [S1]
• Use-after-free — reading *ptr after free(ptr) is explicitly labeled "undefined behavior," not a guaranteed crash — meaning it might appear to work sometimes, making it a particularly dangerous class of bug. [S1]
• Good habits — always initialize variables, use meaningful names, keep indentation clean, keep functions short/focused, verify loop/condition behavior, and read error messages carefully (they often pinpoint the exact problem). [S1]

📖 세부 내용 (Details)

• Missing semicolon (compile-time): int x = 5 printf("%d", x); → error: expected ',' or ';' before 'printf'. [S1]
• Type mismatch (compile-time): int x = "Hello"; → error: initialization makes integer from pointer without a cast. [S1]
• Use-after-free (runtime, undefined behavior): int* ptr = malloc(sizeof(int)); *ptr = 10; free(ptr); printf("%d\n", *ptr); // accessing freed memory. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• 해제된 메모리 접근은 "미정의 동작": free() 이후 포인터를 읽는 것이 항상 크래시로 이어지는 것이 아니라 "undefined behavior"로 명시되어, 우연히 정상 동작하는 것처럼 보일 수도 있어 더 위험하다는 점이 확인됨. [S1]

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — 컴파일 타임 에러 3종과 런타임 에러 3종을 나란히 대비시킨 것이 두 에러 범주의 근본적 차이를 이해하는 실전 학습 자료로 활용된다. [S1]

💻 코드 패턴 (Code patterns)

Using memory after it's been freed — compiles fine, but is undefined behavior at runtime (C):

int* ptr = malloc(sizeof(int));
*ptr = 10;
free(ptr);
printf("%d\n", *ptr); // Undefined behavior - accessing memory that was freed

✅ 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 Date Time, C Memory Deallocate, C Error Handling
• 참조 맥락: 에러 섹션 첫 챕터 — 에러 처리(Error Handling) 챕터로 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — C Errors — https://www.w3schools.com/c/c_errors.php

📝 변경 이력 (Change history)

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