---
id: c-memory-struct
title: "C Structures and Dynamic Memory"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["malloc struct", "array of structs", "realloc struct array", "C 구조체 동적 메모리"]
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", "memory-management", "structs"]
raw_sources: ["https://www.w3schools.com/c/c_memory_struct.php"]
applied_in: []
github_commit: ""
---

# [[C Structures and Dynamic Memory]]

## 🎯 한 줄 통찰 (One-line insight)
Growing a dynamically-allocated array of structs with `realloc()` only extends the ALLOCATION — the newly added slots are explicitly UNINITIALIZED, meaning code that grows a 2-car array to 3 cars must manually `strcpy()`/assign values into the new index (`cars[2]`) before using it, or risk reading garbage; `realloc()` never zero-fills or default-constructs the extra space it creates. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`malloc(sizeof(struct Type))`** — allocates memory for exactly ONE struct instance, accessed via a pointer and the `->` arrow operator. [S1]
- **`malloc(N * sizeof(struct Type))`** — allocates memory for an ARRAY of N structs at once, accessible via normal bracket indexing (`cars[0].brand`). [S1]
- **`strcpy()` still required for string members** — even in dynamically allocated structs, `char[]` fields can't be assigned via `=` and still need `strcpy()`. [S1]
- **Growing with `realloc()` + temporary pointer** — resizing a struct array follows the same safe pattern as the previous chapter (store the result in a temp pointer, check for NULL, only commit on success). [S1]
- **New space from `realloc()` is uninitialized** — expanding from 2 to 3 struct elements leaves the new element's fields with undefined content until explicitly assigned. [S1]

## 📖 세부 내용 (Details)
- Allocating memory for one struct: `struct Car *ptr = (struct Car*) malloc(sizeof(struct Car)); if (ptr == NULL) { ... } strcpy(ptr->brand, "Honda"); ptr->year = 2022; free(ptr);`. [S1]
- Allocating an array of 3 structs at once: `struct Car *cars = (struct Car*) malloc(3 * sizeof(struct Car)); strcpy(cars[0].brand, "Ford"); cars[0].year = 2015;`. [S1]
- Safely growing the array from 2 to 3 elements, then initializing the new slot: `struct Car *tmp = (struct Car*) realloc(cars, newCount * sizeof(struct Car)); if (tmp == NULL) { free(cars); ... } cars = tmp; strcpy(cars[2].brand, "Kia"); cars[2].year = 2022;` — the new element MUST be manually initialized since realloc leaves it undefined. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **realloc으로 늘어난 공간은 초기화되지 않음**: 배열을 2개에서 3개로 늘려도 새로 생긴 3번째 요소의 필드는 값이 정의되지 않은 상태이므로, 사용 전에 반드시 직접 초기화(strcpy/대입)해야 한다는 점이 명시적으로 경고됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
자동차 대수가 고정되지 않은 중고차 딜러십 프로그램에서 필요한 만큼만 구조체 메모리를 동적으로 할당하는 것이 원문에서 직접 실전 활용 사례로 제시됨. [S1]

## 💻 코드 패턴 (Code patterns)
Growing a struct array and initializing the newly added, uninitialized slot (C):
```c
struct Car *tmp = (struct Car*) realloc(cars, newCount * sizeof(struct Car));
if (tmp == NULL) {
  free(cars);
  printf("Reallocation failed.\n");
  return 1;
}
cars = tmp;
// Must manually initialize the new element — realloc leaves it undefined
strcpy(cars[2].brand, "Kia");
cars[2].year = 2022;
```

## ✅ 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 Memory Reallocate]], [[C Structs Pointers]], [[C Memory RealLife]]
- **참조 맥락:** 구조체 동적 메모리 — 메모리 관리 실전 예제(Memory RealLife) 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — C Structures and Dynamic Memory — https://www.w3schools.com/c/c_memory_struct.php

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "C Structures and Dynamic Memory" page (Astra wiki-curation, P-Reinforce v3.1 format).