Question

Here’s my code:

#include<stdio.h>

void main()
{
    FILE *fp;
    fp=fopen("text.txt","r");
    if(fp==NULL)
        printf("ahaha");

    struct karan{
        int index;
        int number;
        char string[10];
    };

    struct karan first;

    fscanf(fp,"%d %d %s",first.index,first.number,first.string);
    printf("%d %d %s",first.index,first.number,first.string);
}  

If my text file contains

1 123 karan
2 1234 haha

When i compile the code it says
Possible use of first before definition.

and on running the code it says
Cannot create process!
What am i doing wrong?

Answer 1

You need to use the & operator with fscanf.

fscanf(fp,"%d %d %s",first.index,first.number,first.string); /* Wrong. */
fscanf(fp,"%d %d %9s", &first.index, &first.number, first.string); /* Right. */
                  ^

Otherwise you’ll be treating the junk in first as addresses and will incur undefined behavior. Also, do note the format for first.string.

There is a C FAQ

Why doesn’t the call scanf(“%d”, i) work?

The arguments you pass to scanf must always be pointers: for each
value converted, scanf “returns” it by filling in one of the
locations you’ve passed pointers to.