CODEWITHSUNDEEP
cfile
Kleiver Marcano
Kleiver Marcano

Reputation: 37

Segmentation fault when trying to write to a file

I was learning about linked list and how to use it, and i make a simple program that store and prints the age and the name of a studen with this approach. i wanted to do other thing, and i thought to store this data from the students inside a text file. But when i try to write to this file, it throws an semengation fault error.

here is the code:

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

typedef struct student {
      char * name;
      int age;
      struct student *next;
}student;

student * createStudent(char *, int);
student * append(student *, student *);
void printStudents(student *, int);
void storeStudents(student *, int, int flag);

int main(){
    student *end, *start , *newStudent, *tmp;
    int studentAge, nStudents, i = 1;
    char * studentName = (char *)malloc(sizeof(char) *50);
    if(!studentName){
        printf("Couldn't allocate the memory\n");
        exit(EXIT_FAILURE);
    }
    printf("Enter the number of students : ");
    scanf("%d", &nStudents);
    while(nStudents > 0){
        printf("Enter the age from the %d student: ", i);
        scanf("%d", &studentAge);
        printf("Enter the name from the %d student: ", i);
        scanf("%s", studentName);
         if((i-1) ==0){
            start = createStudent(studentName, studentAge);
            end = start;
            storeStudents(start, i , 0);
            printStudents(start, i);
        }else{
            newStudent = createStudent(studentName, studentAge);
            end = append(end, newStudent);
            storeStudents(end, i , 1);
            printStudents(end, i);
        }
        nStudents--;
        i++;
    }
    tmp = start -> next;
    free(start);
    start = tmp;
    tmp = start->next;
    free(start);
    free(tmp);
    return 0;
}

void printStudents(student * start, int i){
    if(start != NULL) printf("Student number %d\nName: %s\nAge: %d\n", i, start -> name, start -> age);
    return;
}

void storeStudents(student * ptr, int i, int flag){
    FILE *pfile = NULL;
    switch (flag){
    case 0: pfile = fopen("students.txt", "w+"); break;
    case 1: pfile = fopen("students.txt", "a+"); break;  
    }
    if(!pfile){
        fprintf(stderr, "Couldn't open the file\n");
        exit(EXIT_FAILURE);
    }
    else if(ptr != NULL){
        fprintf(pfile, "Student number %d\nName: %s\nAge: %s\n", i, ptr -> name, ptr -> age);
    }
    fclose(pfile);
    pfile = NULL;
    return;
}

student * createStudent(char * name, int age){
    student * ptr = NULL;
    ptr = (student *) malloc(sizeof(student));
    ptr->name = (char *)malloc(sizeof(char) *50);
    if(!ptr || !(ptr ->name)){
        printf("Couldn't allocate the memory\n");
        exit(EXIT_FAILURE);
    }
    ptr-> age = age;
    ptr ->name = name;
    ptr ->next = NULL;
    return ptr;
}

student * append(student * end, student * new){
    end->next = new;
    end = new;
    return end;
}

the error occurs in the function storeStudents.

what is causing this error?

Upvotes: 1

Views: 52

Answers (1)

Michael Dorgan
Michael Dorgan

Reputation: 12515

Ok, I ran this code with an online C compiler / debugger and it told me the segfault is on the fprintf() line where you have mismatched your types string / int type on age output.

This in combination with your createStudent not doing a string copy and not freeing all your malloc'd memory all are contributing bugs in your application.

I re-ran your code with:

fprintf(pfile, "Student number %d\nName: %s\nAge: %d\n", i, ptr -> name, ptr -> age);

and it no longer segfaults.

Please fix the other issues as well though.

Upvotes: 2

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