在C中读取struct时fscanf崩溃

Question

I am developing some C app for my homework and I'm facing with annoying crash. Here's my code:

#include <stdio.h>
#include <stdlib.h>

//Constants
//Available user choices
enum commands {READ_LIST = 1, QUIT};

struct student {
    char* surname;
    char* name;
    char* group;
};

typedef struct student Student;
typedef Student * studentPtr;

//Globals
int studentCount = 0;

//Function declarations
void displayCommands();
void readList();

//Main function
int main() {

    char enteredValue[999];
    int thisCommand;
    int running = 1;

    while(running) {
        displayCommands();
        scanf("%s", enteredValue);
        thisCommand = atoi(enteredValue);
        puts("\n----------------------------------------------");
        switch(thisCommand) {
            case READ_LIST:
                readList();
                break;
            case QUIT:
                running = 0;
                break;
            default:
                puts("Wrong command!");
                break;
        }
    }
    system("pause");
    return 0;
}

void displayCommands() {
    puts("\n---------------------------------------------");
    puts("Enter a command number:");
    printf("%d - Read students from file.\n", READ_LIST);
    printf("%d - Quit.\n", QUIT);
    puts("----------------------------------------------");
}

void readList() {
    FILE *fp = NULL;

    fp = fopen("studs.txt", "r");

    studentPtr newStudentPtr = malloc(sizeof(Student));

    if(fp != NULL) {
        fscanf(fp, "%d", &studentCount);

        if(newStudentPtr != NULL) {
            fscanf(fp, "%s %s %s", newStudentPtr->surname,
                   newStudentPtr->name, newStudentPtr->group);
        }
        fclose(fp);
    } else {
        puts("Unable to open file for reading!");
    }
}

I basically try to read integer ant three strings into a structure. The program crashes when it's trying to read last line of the file.

Any help, please? What mistakes am I making?

Thanks in advance!

Answer 1

You cannot read into an arbitrary memory address. After you allocate memory to the student structure you also need to allocate memory for each string. Crudely:

    if(newStudentPtr != NULL) {
        char buffer[3][256];
        fscanf(fp, "%s %s %s", buffer[0], buffer[1], buffer[2]);
        newStudentPtr->surname = malloc(strlen(buffer[0])+1);
        strcpy(newStudentPtr->surname, buffer[0]);
        newStudentPtr->name = /* similar ... */;
        newStudentPtr->group = /* similar ... */;
    }

Answer 2

You can change your struct student to contain array of chars (in place of char pointers);

struct student {
    char surname[100];
    char name[100];
    char group[100];
};