C - Nested linked lists

问题

I'm trying to create a linked list of students, each with a linked list of grades, but I'm having trouble accessing the linked list of grades inside the linked list of students.

typedef struct student_data_struct{
    char student[MAX];
    struct grades_list_struct *gradeP;
} student_Data;

typedef struct student_list_struct{
    student_Data studentData;
    struct student_list_struct *next;
} StudentNode;

typedef struct grades_list_struct{
    int grade;
    struct grades_list_struct *next;
} GradeNode;

GradeNode *insertGrade(int grade, GradeNode *head){
    GradeNode *newNode=NULL;
    newNode=(GradeNode*)calloc(1, sizeof(GradeNode));

    if(head!=NULL){
        newNode->grade=grade;
        newNode->next=head;
        return newNode;
    } else {
        newNode->grade=grade;
        newNode->next=NULL;
        return newNode;
    }
}

StudentNode *insertStudent(char studentName[MAX], int studentGrade, StudentNode *head){
    StudentNode *newNode=NULL;
    newNode=(StudentNode*)calloc(1, sizeof(StudentNode));
    newNode->studentData->gradeP=(GradeNode*)calloc(1, sizeof(GradeNode));

    if (head==NULL){
        strcpy(newNode->studentData.student, studentName);
        newNode->next=NULL;
        newNode->studentData->gradeP=insertGrade(studentGrade, newNode->studentData->gradeP);
        return newNode;
    } else {
        strcpy(newNode->student, studentName);
        newNode->gradeP->grade=studentGrade;
        newNode->studentData->gradeP=insertGrade(studentGrade, newNode->studentData->gradeP);
        return newNode;
    }
}

When I try to allocate memory to the grade pointer,

newNode->studentData->gradeP=(GradeNode*)calloc(1, sizeof(GradeNode));

I get the error:

error: invalid type argument of '->' (have 'student_Data' {aka 'struct student_data_struct'})

As well, when I try to insert a grade for a student,

newNode->studentData->gradeP=insertGrade(studentGrade, newNode->studentData->gradeP);

I get the error:

error: invalid type argument of '->' (have 'student_Data' {aka 'struct student_data_struct'})

Any help would be greatly appreciated.

回答1:

You are accessing a struct member with pointer symbol. Try writing as given below:-

newNode->studentData.gradeP=(GradeNode*)calloc(1, sizeof(GradeNode));

newNode->studentData.gradeP=insertGrade(studentGrade, newNode->studentData.gradeP);

回答2:

studentData is of struct type and is not a pointer to a struct. Hence, the member access operator of a struct(.) has to be used instead of an operator to access members of pointer to a struct(->).

来源：https://stackoverflow.com/questions/54812582/c-nested-linked-lists

标签

linked-list

singly-linked-list