Question

My file looks like:

123456789

My code gives me segmentation fault:

#include <stdio.h>

int main(){

    FILE *f; 
    char ch[5];
    f = open("a.txt", "r");
    fgets( ch, 4, f); 
    ch[4] = NULL;
    printf("%s", ch); //Fixed
    return 0;
}

I am an absolute beginner. What am I doing wrong. My aim is to read first 4 characters of the file using fgets.

Answer 1

You’ll want to do

    printf("%s", ch);

For the % format, the argument is a pointer to characters; by passing a single character by value, you’re telling printf to interpret that character’s ASCII value as a pointer, and that’s going to blow up on you; i.e., if the character is a 1, which is ASCII 49, then it’s going to look at byte 49 in memory for a string — and looking down there is generally verboten.

But secondly, I see you’re calling open() instead of fopen(). You must use fopen() or you won’t get a FILE* as you’re expecting.

Both of these individually would likely cause a segfault — you’ll need to fix them both.