CODEWITHSUNDEEP
cprintf
ajishalfred
ajishalfred

Reputation: 277

Why do I get a segmentation fault with my use of printf?

I'm a beginner in C programming. I've trouble using the printf function. When I run the following program I'm getting A segmentation fault. Please tell me what I'm doing wrong. What does a segmentation fault actually mean?

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

typedef struct
{
        char *name;
        int rollnum;
        int marks;
}
student_data;

int main()
{
        student_data stud1;                                             
        student_data *ptr;                                              

        ptr = (student_data *)malloc(sizeof(student_data));


        printf("\n NAME OF THE STUDENT:         " );
        scanf("%s", &ptr -> name);

        printf("\n ROLL NUMBER OF THE STUDENT:  " );
        scanf("%d", &ptr -> rollnum);

        printf("\n MARKS OF THE STUDENT:        " );
        scanf("%d", &ptr -> marks);


        printf("\nPRINTING ROLL NUMBER      %d", ptr -> rollnum);
        printf("\nPRINTING MARKS            %d", ptr -> marks);
        printf("\nPRINTING NAME             %s", ptr -> name);


}

-:output:-

NAME OF THE STUDENT: ajish

ROLL NUMBER OF THE STUDENT: 2

MARKS OF THE STUDENT: 60

PRINTING ROLL NUMBER 2 PRINTING MARKS 60 Segmentation fault

Upvotes: 0

Views: 464

Answers (5)

Yahia
Yahia

Reputation: 70369

You are not initializing ptr -> name which leads to undefined behaviour in the rest of the code using ptr->name.

add ptr->name = (char*) malloc(1000); memset (ptr->name, 0x00, 1000); after malloc and before the first printf.

General remark:

You need to always initialize pointers. When working with scanf you need to be aware that you must allocate/provide enough space to hold whatever might be entered/read (as stated in the documentation) otherwise you get problems with memory management and security and data integrity (like buffer overflows etc.).

Upvotes: 0

Summer_More_More_Tea
Summer_More_More_Tea

Reputation: 13356

You don't allocate storage for ptr->name.

Upvotes: 0

GETah
GETah

Reputation: 21419

You forgot to allocate some memory to student_data.name. As per the scanf documentation, ptr->name should point to an already allocated memory buffer.

Upvotes: 3

Jason S
Jason S

Reputation: 21

scanf("%s", &ptr -> name);

You never allocate ptr->name.

Upvotes: 0

Gabe
Gabe

Reputation: 86718

You never allocate memory for the name.

Upvotes: 1

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