docs(10_Wiki): Dev 폴더 누락분 반영 — Topic_Programming으로 통합

이전 재구성 작업에서 Dev/ 폴더가 누락되었던 것을 반영.

- Dev/Topic_Programming(중첩 폴더, 78개)은 Dev 자체 최상위 폴더들
  (Architecture/Conventions/Engineering_Intelligence 등)과 완전 중복이라 제거.
- Dev 최상위 엔지니어링 지식 폴더(Architecture/Conventions/Engineering_Intelligence/
  Failure_Library/Generalized_Principles/Language/Pattern_Catalog/Platform_Guides/
  Subsystems, 77개)는 이미 Topic_Programming/Topic_Programming에 더 최신 버전이
  존재해 중복 제거(고유 콘텐츠 1개는 예외 처리하여 이동 보존).
- Dev의 W3Schools 언어 튜토리얼 폴더(Topic_C/CPP/CSS/CSharp/HOWTO/HTML/Java/
  JavaScript/PHP/Python/SQL/W3CSS, 1201개)는 전부 Topic_Programming 하위로 이동.
- 에이전트 운영 상태(.astra/docs)는 그대로 유지, 콘텐츠 폴더만 정리.
- Topic_Programming 최종 문서 수: 2784 → 3985.

10_Wiki/Topic_Programming/Topic_C/C_Null.md

@@ -0,0 +1,71 @@
+---
+id: c-null
+title: "C NULL"
+category: "Programming_Language"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["null pointer", "malloc NULL check", "C NULL"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.86
+created_at: 2026-07-04
+updated_at: 2026-07-04
+review_reason: ""
+merge_history: []
+tags: ["c", "programming-language", "w3schools", "null", "pointers"]
+raw_sources: ["https://www.w3schools.com/c/c_null.php"]
+applied_in: []
+github_commit: ""
+---
+
+# [[C NULL]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+`NULL` is the single unifying failure signal shared by two completely unrelated operations — `fopen()` (file access) and `malloc()` (memory allocation) — meaning the SAME defensive pattern (`if (ptr == NULL) { ...handle error... }`) applies whether the resource that might not exist is a file on disk or a block of RAM, because both operations return an ordinary pointer that's simply set to NULL on failure rather than raising any special error mechanism. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **`NULL`** — represents a "null pointer": a pointer that points to nothing/nowhere. [S1]
+- **Failure signal, not an exception** — many C functions (`fopen()`, `malloc()`) return `NULL` when they fail, rather than throwing any error (since C has no exceptions). [S1]
+- **Universal safety check** — comparing any pointer to `NULL` before using it prevents crashes from accessing invalid memory. [S1]
+- **Same pattern across different resources** — the identical `if (ptr == NULL)` check applies whether guarding against a missing file OR a failed memory allocation. [S1]
+
+## 📖 세부 내용 (Details)
+- File-open failure check: `FILE *fptr = fopen("nothing.txt", "r"); if (fptr == NULL) { printf("Could not open file.\n"); return 1; }`. [S1]
+- Memory-allocation failure check (deliberately requesting an absurd amount): `int *numbers = (int*) malloc(100000000000000 * sizeof(int)); if (numbers == NULL) { printf("Memory allocation failed.\n"); return 1; }`. [S1]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+- **NULL 체크는 사용 전 필수 습관**: 크래시를 피하려면 포인터를 사용하기 전 항상 NULL인지 확인해야 한다는 점이 팁으로 강조되며, fopen()과 malloc() 모두 같은 방식으로 실패를 알린다는 공통점이 확인됨. [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+현재 발견된 실제 적용 사례가 없습니다 — 지나치게 큰 메모리를 요청해 malloc()이 실패하는 상황을 의도적으로 재현한 예제가 NULL 체크의 실전 필요성을 직접 보여준다. [S1]
+
+## 💻 코드 패턴 (Code patterns)
+The same NULL-check pattern applying to both file access and memory allocation (C):
+```c
+// File access failure
+FILE *fptr = fopen("nothing.txt", "r");
+if (fptr == NULL) { printf("Could not open file.\n"); return 1; }
+
+// Memory allocation failure
+int *numbers = (int*) malloc(100000000000000 * sizeof(int));
+if (numbers == NULL) { printf("Memory allocation failed.\n"); return 1; }
+```
+
+## ✅ 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 Macros]], [[C Memory Deallocate]], [[C Error Handling]], [[C Newline]]
+- **참조 맥락:** NULL — 줄바꿈(Newline) 챕터로 이어짐.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — C NULL — https://www.w3schools.com/c/c_null.php
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "C NULL" page (Astra wiki-curation, P-Reinforce v3.1 format).