How to allocate memory to a typedef struct within array of structs

Question

I have been trying to allocate memory to the pointer variable but it keeps giving me errors or segmentation fault. How do i properly initialize the pointer variable to the course struct?

 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);
  }

Avoid width-less scanf("%s", student[i]->firstName); string input. Better to use char firstName[10]; .... scanf("%9s", student[i]->firstName); — chux
– chux, Commented Dec 14, 2019 at 7:36

Tofu · Accepted Answer · 2019-10-28 02:44:39Z

You almost had it, there was a few corrections that needed to be made. Course object in Student doesn't need to be a pointer. The array of Student structures need to be dynamically allocated then free'd later on. -> is used as a dereference operator but in your case [] is already dereferencing so you would use . instead of -> and when you allocate memory for the array of structures it needs to be the size of the structure multiplied by the number of structures. 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;
}

I tried to make minimal changes to your code.

Collectives™ on Stack Overflow

How to allocate memory to a typedef struct within array of structs

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related