[C言語] 構造体配列の動的メモリ確保方法と活用例

#include <stdio.h>
// 学生情報を表す構造体
typedef struct {
    char name[50];  // 学生の名前
    int age;        // 学生の年齢
    float gpa;      // 学生のGPA
} Student;

// 学生情報の配列を宣言
Student students[100];

#include <stdlib.h>
// 学生情報の配列を動的に確保
Student *students = (Student *)malloc(100 * sizeof(Student));

// 学生情報の初期化
for (int i = 0; i < 100; i++) {
    snprintf(students[i].name, sizeof(students[i].name), "Student%d", i + 1);
    students[i].age = 20 + i % 5;  // 年齢を20から24の範囲で設定
    students[i].gpa = 3.0 + (i % 10) * 0.1;  // GPAを3.0から3.9の範囲で設定
}
// 学生情報のアクセス
for (int i = 0; i < 100; i++) {
    printf("Name: %s, Age: %d, GPA: %.1f\n", students[i].name, students[i].age, students[i].gpa);
}

// メモリの解放
free(students);

#include <stdio.h>
#include <stdlib.h>
typedef struct {
    char name[50];
    int age;
    float gpa;
} Student;
int main() {
    int num_students = 3;
    Student *students = (Student *)malloc(num_students * sizeof(Student));
    // 学生情報の初期化
    for (int i = 0; i < num_students; i++) {
        snprintf(students[i].name, sizeof(students[i].name), "Student%d", i + 1);
        students[i].age = 18 + i;
        students[i].gpa = 3.5 + i * 0.1;
    }
    // 学生情報の表示
    for (int i = 0; i < num_students; i++) {
        printf("Name: %s, Age: %d, GPA: %.1f\n", students[i].name, students[i].age, students[i].gpa);
    }
    free(students);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
typedef struct {
    char product_name[50];
    int quantity;
    float price;
} Product;
int main() {
    int num_products = 5;
    Product *inventory = (Product *)malloc(num_products * sizeof(Product));
    // 商品情報の初期化
    for (int i = 0; i < num_products; i++) {
        snprintf(inventory[i].product_name, sizeof(inventory[i].product_name), "Product%d", i + 1);
        inventory[i].quantity = 10 + i * 5;
        inventory[i].price = 100.0 + i * 20.0;
    }
    // 商品情報の表示
    for (int i = 0; i < num_products; i++) {
        printf("Product: %s, Quantity: %d, Price: %.2f\n", inventory[i].product_name, inventory[i].quantity, inventory[i].price);
    }
    free(inventory);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
typedef struct {
    char title[100];
    char author[50];
    char isbn[20];
} Book;
int main() {
    int num_books = 4;
    Book *library = (Book *)malloc(num_books * sizeof(Book));
    // 書籍情報の初期化
    for (int i = 0; i < num_books; i++) {
        snprintf(library[i].title, sizeof(library[i].title), "Book Title %d", i + 1);
        snprintf(library[i].author, sizeof(library[i].author), "Author %d", i + 1);
        snprintf(library[i].isbn, sizeof(library[i].isbn), "ISBN%d", 1000 + i);
    }
    // 書籍情報の表示
    for (int i = 0; i < num_books; i++) {
        printf("Title: %s, Author: %s, ISBN: %s\n", library[i].title, library[i].author, library[i].isbn);
    }
    free(library);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
typedef struct {
    char name[50];
    int age;
} Person;
int main() {
    int initial_size = 2;
    Person *people = (Person *)malloc(initial_size * sizeof(Person));
    // 初期データの設定
    for (int i = 0; i < initial_size; i++) {
        snprintf(people[i].name, sizeof(people[i].name), "Person%d", i + 1);
        people[i].age = 20 + i;
    }
    // 配列のサイズを拡張
    int new_size = 4;
    people = (Person *)realloc(people, new_size * sizeof(Person));
    // 新しいデータの追加
    for (int i = initial_size; i < new_size; i++) {
        snprintf(people[i].name, sizeof(people[i].name), "Person%d", i + 1);
        people[i].age = 20 + i;
    }
    // データの表示
    for (int i = 0; i < new_size; i++) {
        printf("Name: %s, Age: %d\n", people[i].name, people[i].age);
    }
    free(people);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct {
    char name[50];
    int age;
} Person;
// 年齢で比較する関数
int compareByAge(const void *a, const void *b) {
    return ((Person *)a)->age - ((Person *)b)->age;
}
int main() {
    int num_people = 3;
    Person people[] = {
        {"Alice", 30},
        {"Bob", 25},
        {"Charlie", 35}
    };
    // 年齢でソート
    qsort(people, num_people, sizeof(Person), compareByAge);
    // ソート結果の表示
    for (int i = 0; i < num_people; i++) {
        printf("Name: %s, Age: %d\n", people[i].name, people[i].age);
    }
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct {
    char name[50];
    int age;
} Person;
// 名前で比較する関数
int compareByName(const void *a, const void *b) {
    return strcmp(((Person *)a)->name, ((Person *)b)->name);
}
int main() {
    int num_people = 3;
    Person people[] = {
        {"Alice", 30},
        {"Bob", 25},
        {"Charlie", 35}
    };
    // 名前でソート
    qsort(people, num_people, sizeof(Person), compareByName);
    // 検索する名前
    Person key = {"Bob", 0};
    Person *found = (Person *)bsearch(&key, people, num_people, sizeof(Person), compareByName);
    if (found != NULL) {
        printf("Found: Name: %s, Age: %d\n", found->name, found->age);
    } else {
        printf("Not found\n");
    }
    return 0;
}