c - 如何将内存分配给结构数组中的 typedef 结构

Question

我一直在尝试为指针变量分配内存，但它一直给我错误或段错误。我如何正确地将指针变量初始化为类(class)结构？

 typedef struct {
    char courseId[7];
    char courseName[10];
    } Course;

    struct Student{
    char firstName[10];
    char lastName[10];
    int studentId;
     Course *course;
    };

int main() {
  int numStudents;
  printf("How many students do you wish to register?: ");
  scanf("%d", &numStudents);
  struct Student *student[numStudents];
  student[numStudents] = malloc(sizeof(*student[numStudents]));
  student[numStudents]->course = malloc(sizeof*(numStudents * Course));
  for (int i = 0; i < numStudents; i++) {
    printf("Enter student #%d First Name: ", i+1);
    scanf("%s", student[i]->firstName);
    printf("Enter student Last Name: ");
    scanf("%s", student[i]->lastName);
    printf("Enter Student ID: ");
    scanf("%d", &student[i]->studentId);
    printf("Enter Course ID: ");
    //student[i]->course = malloc(sizeof(*(student[i]->course)));
    scanf("%s", student[i]->course->courseId);
    printf("Enter Cousrse Name: ");
    //student[i]->course = malloc(sizeof(*(student[i]->course)));
    scanf("%s", student[i]->course->courseName);
  }

  for (int i = 0; i < numStudents; i++) {
    printf("Student Name: %s %s\n", student[i]->firstName, student[i]->lastName);
    printf("Student ID: %d\n", student[i]->studentId);
    printf("Course Code: %s\n", student[i]->course->courseId );
    printf("Course name: %s\n", student[i]->course->courseName);
    free(student[i]->course);
  }

Answer 1

您几乎完成了，需要进行一些更正。Student 中的 Course 对象不需要是指针。 Student 结构数组需要动态分配，然后再释放。 -> 用作取消引用运算符，但在您的情况下 [] 已经取消引用，因此您将使用 . 而不是 -> 当你为结构数组分配内存时，它需要结构的大小乘以结构的数量。 malloc(sizeof(struct Student)*numStudents);

typedef struct {
    char courseId[7];
    char courseName[10];
} Course;

struct Student{
    char firstName[10];
    char lastName[10];
    int studentId;
    Course course;
};

int main() {
    int numStudents;
    printf("How many students do you wish to register?: ");
    scanf("%d", &numStudents);
    struct Student* students = malloc(sizeof(struct Student)*numStudents);
    for (int i = 0; i < numStudents; i++) {
        printf("Enter student #%d First Name: ", i+1);
        scanf("%s", students[i].firstName);
        printf("Enter student Last Name: ");
        scanf("%s", students[i].lastName);
        printf("Enter Student ID: ");
        scanf("%d", &students[i].studentId);
        printf("Enter Course ID: ");
        scanf("%s", students[i].course.courseId);
        printf("Enter Cousrse Name: ");
        scanf("%s", students[i].course.courseName);
    }

    for (int i = 0; i < numStudents; i++) {
        printf("Student Name: %s %s\n", students[i].firstName, students[i].lastName);
        printf("Student ID: %d\n", students[i].studentId);
        printf("Course Code: %s\n", students[i].course.courseId );
        printf("Course name: %s\n", students[i].course.courseName);
    }
    free(students);
    return 0;
}

我尝试对您的代码进行最少的更改。