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10_Wiki/Dev/Topic_C/C_Error_Handling.md

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+---
+id: c-error-handling
+title: "C Error Handling"
+category: "Programming_Language"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["perror strerror errno", "exit EXIT_FAILURE", "C 에러 처리"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.87
+created_at: 2026-07-04
+updated_at: 2026-07-04
+review_reason: ""
+merge_history: []
+tags: ["c", "programming-language", "w3schools", "error-handling", "errno"]
+raw_sources: ["https://www.w3schools.com/c/c_error_handling.php"]
+applied_in: []
+github_commit: ""
+---
+
+# [[C Error Handling]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+C has NO try/catch mechanism at all — the source states this directly — meaning every error-handling technique in this chapter (checking for `NULL` returns, `perror()`, `strerror(errno)`, comparing `errno` to constants like `ENOENT`) is a WORKAROUND built from ordinary control flow (if-statements and return values), not a language feature, which is why disciplined manual NULL-checking after every risky operation is non-negotiable in C in a way it isn't in exception-based languages. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **No built-in exceptions** — C lacks try/catch; error handling relies on return values, global error codes (`errno`), and helper functions. [S1]
+- **NULL-return checking** — many functions (like `fopen()`) return `NULL` on failure; checking with `if (ptr == NULL)` is the primary detection mechanism. [S1]
+- **`perror(message)`** — prints a custom message plus a system-provided description of the last error. [S1]
+- **`errno` + `strerror(errno)`** — `errno` (from `<errno.h>`) holds the last failed operation's error code; `strerror()` converts it to a readable string. [S1]
+- **Named error constants** — `ENOENT` (no such file/directory), `EACCES` (permission denied), `ENOMEM` (out of memory), `EINVAL` (invalid argument) — allow branching on the SPECIFIC failure reason. [S1]
+- **`exit(code)`** — immediately terminates the program with a status code; `0`/`EXIT_SUCCESS` means success, non-zero/`EXIT_FAILURE` signals an error to the OS. [S1]
+
+## 📖 세부 내용 (Details)
+- Basic NULL check: `FILE *fptr = fopen("nothing.txt", "r"); if (fptr == NULL) { printf("Error opening file.\n"); return 1; }`. [S1]
+- Detailed error via `perror()`: `perror("Error opening file"); // "Error opening file: No such file or directory"`. [S1]
+- Branching on a specific error code: `if (errno == ENOENT) { printf("The file was not found.\n"); } else { printf("Some other file error occurred.\n"); }`. [S1]
+- Exiting cleanly with readable status constants: `if (f == NULL) { perror("Could not open nothing.txt"); exit(EXIT_FAILURE); } return EXIT_SUCCESS;`. [S1]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+- **C에는 try/catch가 없음**: 다른 언어와 달리 예외 처리 메커니즘이 아예 없고, 반환값·errno·perror()/strerror() 같은 도구를 조합해 직접 에러를 감지하고 대응해야 한다는 점이 명시적으로 확인됨. [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+존재하지 않는 파일(nothing.txt)을 열려는 시도가 실패하는 상황을 NULL 체크, perror(), strerror(errno), errno 비교, exit() 등 다섯 가지 방식으로 반복 제시하며 각 기법의 실전 활용을 직접 보여줌. [S1]
+
+## 💻 코드 패턴 (Code patterns)
+Detecting a specific error condition via errno and reporting it with a custom message (C):
+```c
+#include <errno.h>
+FILE *f = fopen("nothing.txt", "r");
+if (f == NULL) {
+  if (errno == ENOENT) {
+    printf("The file was not found.\n");
+  } else {
+    printf("Some other file error occurred.\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:** 0.87
+- **중복 검사 결과:** 신규 생성 (New discovery)
+
+## 🔗 지식 그래프 (Knowledge Graph)
+- **상위/루트:** [[C Tutorial]]
+- **관련 개념:** [[C Errors]], [[C Null]], [[C Input Validation]]
+- **참조 맥락:** 에러 처리 — 입력 검증(Input Validation) 챕터로 이어짐.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — C Error Handling — https://www.w3schools.com/c/c_error_handling.php
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "C Error Handling" page (Astra wiki-curation, P-Reinforce v3.1 format).