[C言語] 構造体とポインタ配列の効果的な使い方

#include <stdio.h>
#include <stdlib.h>
// 構造体の定義
typedef struct {
    int id;
    char name[50];
} Student;
int main() {
    // 構造体ポインタ配列の宣言
    Student *students[3];
    // メモリの動的割り当てと初期化
    for (int i = 0; i < 3; i++) {
        students[i] = (Student *)malloc(sizeof(Student));
        students[i]->id = i + 1;
        sprintf(students[i]->name, "Student%d", i + 1);
    }
    // データの表示
    for (int i = 0; i < 3; i++) {
        printf("ID: %d, Name: %s\n", students[i]->id, students[i]->name);
    }
    // メモリの解放
    for (int i = 0; i < 3; i++) {
        free(students[i]);
    }
    return 0;
}

ID: 1, Name: Student1
ID: 2, Name: Student2
ID: 3, Name: Student3

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// レコードを表す構造体
typedef struct {
    int id;
    char name[50];
    double balance;
} Account;
// レコードの追加
void addRecord(Account **accounts, int *size, int id, const char *name, double balance) {
    accounts[*size] = (Account *)malloc(sizeof(Account));
    accounts[*size]->id = id;
    strcpy(accounts[*size]->name, name);
    accounts[*size]->balance = balance;
    (*size)++;
}
int main() {
    Account *accounts[10];
    int size = 0;
    // レコードの追加
    addRecord(accounts, &size, 1, "Alice", 1000.0);
    addRecord(accounts, &size, 2, "Bob", 1500.0);
    // レコードの表示
    for (int i = 0; i < size; i++) {
        printf("ID: %d, Name: %s, Balance: %.2f\n", accounts[i]->id, accounts[i]->name, accounts[i]->balance);
    }
    // メモリの解放
    for (int i = 0; i < size; i++) {
        free(accounts[i]);
    }
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// 構造体の定義
typedef struct {
    int id;
    char name[50];
} Person;
// 比較関数
int compareByName(const void *a, const void *b) {
    Person *personA = *(Person **)a;
    Person *personB = *(Person **)b;
    return strcmp(personA->name, personB->name);
}
int main() {
    Person *people[3];
    people[0] = (Person *)malloc(sizeof(Person));
    people[1] = (Person *)malloc(sizeof(Person));
    people[2] = (Person *)malloc(sizeof(Person));
    // データの初期化
    people[0]->id = 1; strcpy(people[0]->name, "Charlie");
    people[1]->id = 2; strcpy(people[1]->name, "Alice");
    people[2]->id = 3; strcpy(people[2]->name, "Bob");
    // ソート
    qsort(people, 3, sizeof(Person *), compareByName);
    // ソート結果の表示
    for (int i = 0; i < 3; i++) {
        printf("ID: %d, Name: %s\n", people[i]->id, people[i]->name);
    }
    // メモリの解放
    for (int i = 0; i < 3; i++) {
        free(people[i]);
    }
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// 構造体の定義
typedef struct {
    int id;
    char name[50];
} Record;
int main() {
    Record *records[2];
    records[0] = (Record *)malloc(sizeof(Record));
    records[1] = (Record *)malloc(sizeof(Record));
    // データの初期化
    records[0]->id = 1;
    strcpy(records[0]->name, "Data1");
    records[1]->id = 2;
    strcpy(records[1]->name, "Data2");
    // ファイルへの書き込み
    FILE *file = fopen("data.txt", "w");
    for (int i = 0; i < 2; i++) {
        fprintf(file, "ID: %d, Name: %s\n", records[i]->id, records[i]->name);
    }
    fclose(file);
    // メモリの解放
    for (int i = 0; i < 2; i++) {
        free(records[i]);
    }
    return 0;
}